Credit…Jose A. Alvarado Jr. for The New York Times

The Centers for Disease Control and Prevention recommended Sunday that no mass gatherings with 50 people or more — including weddings, festivals, parades, concerts, sporting events or conferences — be held in the United States for the next eight weeks in one of the federal government’s most sweeping efforts to slow the spread of the coronavirus.

The C.D.C. said that its recommendation, which would dramatically change life in the United States for the next two months, does not apply to “the day to day operation of organizations such as schools, institutes of higher learning, or businesses” and added that it was not intended to supersede the advice of local health officials.

“This recommendation is made in an attempt to reduce introduction of the virus into new communities,” it said, “and to slow the spread of infection in communities already affected by the virus.”

And the C.D.C. urged people to take care with even small gatherings. “Events of any size should only be continued if they can be carried out with adherence to guidelines for protecting vulnerable populations, hand hygiene and social distancing,” its recommendation said. “When feasible, organizers could modify events to be virtual.”

The Federal Reserve slashed interest rates to near-zero and unveiled a sweeping set of programs — including plans to snap up huge amounts of government and mortgage-backed debt — in an effort to backstop the United States economy as the spread of coronavirus poses a dire threat to economic growth.

“The coronavirus outbreak has harmed communities and disrupted economic activity in many countries, including the United States,” the central bank said in a statement on Sunday. “The Federal Reserve is prepared to use its full range of tools to support the flow of credit to households and businesses.”

At a news conference on Sunday afternoon, President Trump congratulated the Federal Reserve for its slashing rates to nearly zero.

“It makes me very happy,” he said.

Lowering interest rates is supposed to help goose the economy by making it cheaper for households and businesses to borrow money, which they will hopefully use to buy houses, cars and invest in new plants and equipment.

Besides cutting its key interest rate by a full percentage point, returning it to a range of 0 to 0.25 percent, the Fed said that it would increase its holdings of Treasury securities by at least $500 billion and its holdings of government mortgage-backed securities by at least $200 billion “over coming months.”

“The committee will continue to closely monitor market conditions and is prepared to adjust its plans as appropriate,” it said.

The Fed also encouraged banks to use its discount window, which provides ready access to financing, and said it was “encouraging banks to use their capital and liquidity buffers as they lend to households and businesses.” The Fed also eliminated bank reserve requirements — a suite of efforts meant to free up cash for the banks to keep lending.

New York City’s public school system, the nation’s largest with 1.1 million students, will begin shutting down this week, Governor Andrew M. Cuomo said on Sunday, in what is the city’s most aggressive and disruptive effort to slow the spread of the coronavirus.

Public schools in Long Island and Westchester will also close this week, the governor said.

The city and union leaders are working on plans for emergency child care for essential city workers whose children attend public schools. Mr. Cuomo said earlier on Sunday that any decision to close New York City’s schools must include a plan to allow parents who are health care workers to continue to report to hospitals.

City Hall also announced on Sunday night that it would order all bars and restaurants to close. Restaurants would be limited to takeout and food delivery, officials said.

More than a dozen states have already closed schools, creating concerns that children may miss meals and parents may not be able to stay home from work. On Sunday, Gov. Gavin Newsom of California said school closures now affect 80 to 85 percent of all schoolchildren in his state.

After Los Angeles Unified School District said that it was closing, school officials said they would open 40 family resource centers to provide child care and meals to students whose parents cannot get out of work. North Carolina closed its public schools on Saturday.

The decision to close New York City’s schools came after the mayor faced increasing pressure throughout the day, including from the governor. Mr. Cuomo said in an interview with The New York Times on Sunday afternoon that the schools should close “as soon as Monday or Tuesday or Wednesday.”

“I believe that the New York City schools should be closed, period,” he said. “We also need an immediate plan to provide child care for essential workers and for food programs for the children.”

The highly influential union that represents New York City’s public health care workers, 1199SEIU, reversed course on Sunday and called on the mayor to close the city’s public schools. The union had been the only major union supporting his decision to keep schools open.

The city’s libraries closed, too. The Queens and Brooklyn Public Library systems announced Sunday evening that they would close beginning Monday, following the example set earlier by the New York Public Library.

As they faced off in a debate that was transformed in ways both large and small by the coronavirus pandemic, the two rivals for the Democratic presidential nomination, former Vice President Joseph R. Biden Jr. and Senator Bernie Sanders of Vermont, both agreed on at least one thing: a greater role for the United States military in helping the nation deal with the outbreak.

“I would call up the military now,” Mr. Biden said. “They have the capacity to provide the surge help that hospitals need and is needed across the nation.”

Mr. Sanders was slightly less direct, but agreed. “Using the National Guard is clearly something that needs to be done,” he said.

Both men said that the pandemic was highlighting weaknesses in the health care system. Mr. Biden warned that it was ill-equipped to handle the expected surge of coronavirus cases, saying, “We should be planning where we are going to put these temporary hospitals.”

Mr. Sanders, meanwhile, said that it was highlighting the shortcomings of America’s for-profit health industry. “Let’s be honest and understand that this coronavirus pandemic exposes the incredible weakness and dysfunctionality of our current health care system,” he said.

Both men — Mr. Biden is 77, and Mr. Sanders, 78 — said that they were taking steps during the campaign to avoid contracting the virus, including canceling events, using hand sanitizer and washing their hands regularly.

“I am using a lot of soap and hand sanitizers,” Mr. Sanders said.

“I wash my hands I don’t know how many times a day with hot water and soap,” Mr. Biden said.

The coronavirus shaped not just the content of the debate, but its format, too. The face-off was moved to Washington, D.C., from Phoenix over concerns about the outbreak. There was no live audience, in an effort to promote the social distancing health experts are calling for. The candidates parried from lecterns that were kept six feet apart. And when they took the stage, they dispensed with the customary handshake in favor of a coronavirus-era elbow bump.

California called for all people 65 and older to shelter in their homes. Massachusetts moved to ban dining in bars and restaurants beginning Tuesday, effectively closing Boston’s bars for St. Patrick’s Day. And Puerto Rico set some of the strictest measures in the United States, imposing a 9 p.m. to 5 a.m. curfew and closing nonessential businesses.

As the number of coronavirus cases in the United States climbed to over 3,100 across 49 states on Sunday, and after weeks of conflicting signals from the federal government, state and local officials across the nation began enacting stricter measures to try to slow the virus’s spread.

Massachusetts said that beginning Tuesday bars and restaurants would only be able to offer takeout and delivery only, banned gatherings of more than 25 people and ordered all public and private schools to close Tuesday.

“I realize these measures are unprecedented,” Gov. Charlie Baker of Massachusetts said Sunday night, “but we’re asking our residents to take a deep breath and understand the rationale behind this guidance.”

Washington State announced it was shutting down restaurants and bars (except for delivery and takeout), and entertainment venues and recreational facilities. The new mandates from Gov. Jay Inslee will also require reduced occupancy for retail outlets.

The state of Ohio ordered restaurants and bars to close as of 9 p.m. Sunday, but said it would allow food to be carried out and delivered. Maryland’s governor ordered casinos, racetracks and betting facilities to close “indefinitely.”

Even as public health experts were publicly urging social distancing, Representative Devin Nunes, Republican of California, went on Fox News and encouraged healthy people to dine out at restaurants. “Likely you can get in easily,” he said. “Let’s not hurt the working people in this country that are relying on wages and tips to keep their small business going.”

And Oklahoma’s governor was criticized on social media after sharing a selfie on Twitter Saturday of him with his children having dinner at a packed food hall in the heart of Oklahoma City. In the since-deleted tweet, he captioned the photo with, “Eating with my kids and all my fellow Oklahomans at the @CollectiveOKC. It’s packed tonight! #supportlocal #OklaProud.”

The scope of the public health crisis became even clearer over the weekend as officials in Louisiana, New York and Virginia reported their first deaths tied to the coronavirus. Only West Virginia was without a single diagnosis.

In the Omaha, Neb., area, officials reported the first known instance of community spread. In Illinois, a nursing facility where a woman tested positive was placed on lockdown. And in Pittsburgh, where the first local cases were announced on Saturday, city leaders urged bars to limit the number of people they allowed inside.

New York City officials advised all members of the United Nations diplomatic community that they should assume they have been exposed to the coronavirus, should practice the “maximum-possible social distancing” and should not expect any special accommodations if they are sickened, according to a memo of a teleconference briefing shared by diplomats.

Two American emergency-room doctors — one in Washington State and one in New Jersey — were in critical condition with Covid-19, the disease caused by the coronavirus, the American College of Emergency Physicians said on Saturday. Dr. William Jaquis, the organization’s president, said it was unclear whether the doctor in Washington, who is in his 40s, had contracted the virus at the hospital. The physician in Paterson, N.J., who is 70, had been leading his hospital’s emergency preparedness.

Authorities in Texas began preparing judges for the possibility that they may have to be ready to order the quarantine of coronavirus patients who refuse to isolate themselves.

Despite the clearing out of grocery store shelves in recent days, the nation’s biggest retailers, dairy farmers and meat producers said the food supply chain remains intact and has been ramping up to meet the unprecedented stockpiling brought on by the coronavirus pandemic.

At the news conference on Sunday afternoon, Mr. Trump said he had a phone call with chief executives of several food suppliers who said they were committed to staying open through the coronavirus pandemic. He said the call was “very reassuring” and said there was no need to “hoard” essential food supplies.

“You don’t have to buy so much, take it easy, just relax,” Mr. Trump said. “We’re doing great, it all will pass.”

The coronavirus continued its assault on Italy, the hardest hit country outside of China, with officials on Sunday reporting the number of deaths rose to 1,809 — a 25 percent increase over the day before and the largest one-day uptick yet of any country.

The 368 deaths Italy reported exceeds the highest single-day number China reported at the height of its outbreak. China’s highest daily toll was on Feb. 13, when the country reported 254 new deaths, according to the World Health Organization.

The staggering caseload in Italy topped 24,700, even as the entire country has been locked down for a week, an escalation that is only likely to increase, raising urgent questions about how overloaded hospitals, particularly the hard-hit north, will cope.

The Vatican said on Sunday that its traditional services during the week before Easter, which usually draw tens of thousands of people, would not be open to the public next month, interrupting a historic tradition.

Germany will close its borders with Austria, Denmark, France, Luxembourg and Switzerland in an effort to slow the spread of the coronavirus, the country’s interior minister said on Sunday, following several other European Union member states in restricting the freedom of movement across the continent.

Spain and France announced drastic countrywide restrictions this weekend. The countries are the hardest hit after Italy.

On Sunday, Spanish officials reported nearly 8,000 cases of coronavirus and 288 deaths. The country ordered all residents to confine themselves to their homes — and to leave only to buy food, go to work, seek medical care or assist older people and others in need. The government also ordered all schools, restaurants and bars to close.

The Spanish authorities said that the prime minister’s wife, Begoña Gómez, had tested positive for the virus.

France announced the closing of all “non-indispensable” businesses, including restaurants, bars and movie theaters, after a sharp uptick in coronavirus cases. The number of French cases passed 5,420 on Sunday, with 127 deaths. On Saturday, 300 coronavirus patients were in critical condition — half of them under 60 years of age.

On Sunday, France’s transportation minister said the country would begin reducing plane, train and bus services between cities.

Argentina’s president, Alberto Fernández, announced on Sunday night that the country would shut down its borders for inbound foreigners for at least 15 days — one of the most drastic measures taken by a government seeking to keep the virus from spreading in a region that has relatively few diagnosed cases. Schools will close until at least the end of the month and cinemas, theaters and sporting events are canceled, he said.

“This is a war against an invisible enemy,” Mr. Fernández said in a televised address.

One after another, countries around the world on Sunday continued to implement extraordinary measures as they raced to contain the spread of the coronavirus, closing schools, shuttering restaurants and bars, mandating quarantines and severely limiting travel.

  • China’s capital, Beijing, is toughening its rules for international arrivals, requiring everyone coming from overseas to spend the mandatory 14-day isolation at a quarantine site that they will be required to pay for.

  • South Africa declared a national state of disaster, closing schools, shutting down ports and banning gatherings of more than 100 people. South African citizens returning from other some high-risk countries will be tested and face quarantines. The government is strengthening surveillance and testing systems.

  • Austria banned gatherings of more than five people and imposed steep fines for those who disobeyed a far-reaching curfew. Public parks, sporting fields and restaurants will close from Monday, and fines for violations are up to 3,600 euros. Travelers from Britain, the Netherlands, Russia and Ukraine are being added to a lengthening list of those banned from entering Austria.

  • Ireland is closing its pubs for two weeks, including on St. Patrick’s Day, and barring gatherings of more than 100 people.

  • The Netherlands announced a lockdown that will last until April 6, closing schools and child care facilities. Restaurants, cafes, gyms and sporting clubs will also be closed.

  • Manila, the densely populated capital of the Philippines, went under lockdown. Public gatherings are banned and classes suspended for a month; travel in and out of the Manila metropolitan area is restricted; and soldiers and police officers have set up traffic checkpoints to take people’s temperatures. Some in the country fear a return to a Marcos-style dictatorship.

A top health official said on Sunday that stronger efforts to slow the spread of the coronavirus would roll out over the next several weeks, a period he characterized as crucial for controlling the outbreak.

Appearing across a number of Sunday morning news programs, Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, said that travel bans enacted last week have helped curb transmission, but that U.S. citizens would have to make personal sacrifices and comply with government guidelines to avoid a “worst-case scenario.”

On NBC’s “Meet the Press,” Dr. Fauci cautioned, “Americans should be prepared that they are going to have to hunker down significantly more than we as a country are doing.”

Underscoring the risk that the virus poses to the nation’s front-line medical workers, two emergency medicine doctors, in New Jersey and Washington State, are in critical condition as a result of the coronavirus, the American College of Emergency Physicians said.

While the Trump administration has banned international travelers coming from high-risk countries and regions, such as China, Iran, and much of Europe, Dr. Fauci said domestic travel restrictions hadn’t been seriously discussed.

“I don’t see that right now or in the immediate future,” he said on “This Week.” “But remember, we are very open-minded about whatever it takes to preserve the health of the American public.”

In an interview with Brianna Keilar on CNN, Dr. Fauci said that progress was being made with companies like Walmart and CVS to improve diagnostic and testing capabilities. But he cautioned that disruptions to daily life were likely to continue.

“For a while, life is not going to be the way it used to be in the United States,” he said. “We have to just accept that if we want to do what’s best for the American public.”

Meanwhile, Daniel Goldman, who as the top investigator for the House Intelligence Committee played a leading role in the impeachment of Mr. Trump, has tested positive, a House official confirmed on Sunday.

Mr. Goldman left the committee earlier this month. The panel’s chairman, Representative Adam B. Schiff of California, said Sunday that neither he nor any of his other aides were exhibiting symptoms. Mr. Schiff had already canceled public events and directed his staff to work from home.

As the U.S. government rushed on Saturday to implement Mr. Trump’s restrictions on travel from Europe, part of an effort to stop the spread of the coronavirus, chaos ensued at some of America’s biggest airports.

In Dallas, travelers posted photos on Twitter of long winding lines in the airport. In New York, customs agents in paper and plastic masks boarded a flight from Paris. And in Chicago, where travelers reported standing in line for hours, Gov. J.B. Pritzker of Illinois tagged Mr. Trump in a series of angry tweets about the long waits, saying, “The federal government needs to get its s@#t together. NOW.”

Paige Hardy, an American student who left behind her graduate studies in London because she feared a broader travel ban, said a series of confusing announcements in the air and upon landing in Dallas led to alarm on the plane late Saturday. She posted a video on Twitter of travelers being asked to raise their hands if they had been in mainland Europe. Because of the delay, she also missed her connecting flight.

“It truly felt like an apocalyptic scenario,” said Ms. Hardy, who left many of her belongings behind in England and was unsure whether she would be able to return.

The confusion came as concern spread about the coronavirus pandemic, which has now been identified in more than 2,700 people in the United States and has prompted Mr. Trump to declare a national emergency.

“At this time, we are working quickly with our partners to operationalize a plan which will outline where these travelers will be routed and what the screening process will be,” said Marcus Hubbard, a spokesman for the Centers for Disease Control and Prevention.

Chad Wolf, the acting secretary of Homeland Security, said on Twitter that he was aware of the delays and was working to add staffing.

American Airlines said on Saturday that it would suspend almost all of its long-haul international flights beginning Monday in response to decreased demand. The airline said the suspensions would last until at least May 6 and would represent a 75 percent decline in international capacity compared with the same period last year.

Treasury Secretary Steven Mnuchin said on Sunday that he would ask Congress to reinstate powers that were used during the 2008 financial crisis to support the economy as the coronavirus threatens to grind U.S. business activity to a halt.

The comments suggest that the White House is bracing for a widespread downturn that could harm sectors well beyond the travel and cruise ship industries, and that the federal government could need to return to the type of crisis-era measures that were ultimately scaled back by lawmakers in the 2010 Dodd-Frank Act.

Mr. Mnuchin and Jerome H. Powell, the chairman of the Federal Reserve, have been in daily conversations about how to buttress the economy, which faces the prospect of a deep recession as the coronavirus spreads around the world.

“Certain tools were taken away that I’m going to go back to Congress and ask for,” Mr. Mnuchin said on “This Week” on ABC.

In a separate interview on Fox News Sunday, Mr. Mnuchin made clear that he was talking about regulations that were imposed by Dodd-Frank.

That law, passed in the wake of the worst financial crisis in decades, took away the Fed’s power to lend to individual failing firms or to take assets off their balance sheets, requiring the central bank to extend emergency credit only through broad-based facilities designed to help the financial system as a whole. Congress also took away Treasury’s ability to use a program, known as the Exchange Stabilization Fund, to guarantee money market funds.

Starbucks said Sunday it was moving to a “to go” model for at least two weeks in the U.S. and Canada to encourage social distancing.

Customers will not be permitted to sit in the cafe or patio areas, but can still walk up and order at the counter, through the Starbucks app, via the drive-through and by delivery. Stores located in communities with high clusters of cases and high-social gathering locations, such as malls and university campuses, would be closed temporarily, the company said in a statement.

LVMH, the French company known for luxury items, said Sunday that it would redirect its cosmetic division to produce mass quantities of hydroalcoholic gel and give it to French health authorities.

The company said in a statement that it would use the facilities where it produces fragrances under the Christian Dior, Givenchy and Guerlain labels to make the sanitizing products starting Monday.

Some retailers and luxury hotels have also been closing their doors.

On Sunday, Nike said it would shut all of its stores in the United States, Canada, Western Europe, New Zealand and Australia from Monday until March 27, and Wynn Resorts said it would temporarily close Wynn Las Vegas and Encore, two luxury hotel towers encompassing thousands of hotel rooms, casino space and spas, for at least two weeks starting on Tuesday. On Saturday, Urban Outfitters said that it would shut all of its stores until further notice, and Apple said it would close its stores outside mainland China, Hong Kong and Taiwan for two weeks.

As countries across Europe impose lockdowns and restrict travel, Prime Minister Boris Johnson of Britain is facing a swelling tide of opposition to his government’s more relaxed measures to stem the coronavirus.

In an open letter, nearly 350 scientists and doctors called on him to immediately impose the kind of social distancing steps that countries like Italy, France and Spain have adopted.

They warned that Britain’s approach — in which the government has talked of impending moves like quarantining older residents and closing schools but pushed off the timing for 10 days or longer — was putting lives at risk.

Health Secretary Matt Hancock told the British broadcaster Sky News that the action plan under consideration including asking Britons over 70 to self-isolate for up to four months to reduce their risk of contracting the virus. The government is also expected to ban large gatherings starting next week and to order people over age 70 to remain at home.

The rate of infection in the country has been climbing as rapidly as elsewhere in Europe. Britain had at least 1,370 confirmed cases and 35 deaths as of Sunday, and the United States this weekend extended its ban on travelers from most of Europe to include those coming from Britain, as well.

On Sunday, Britain’s Foreign and Commonwealth Office also advised against “all but essential travel to the U.S.A., due to restrictions put in place by the U.S. government” on foreign nationals arriving from Britain and Ireland from Monday.

An Italian ship on a trans-Atlantic voyage has become the cruise industry’s latest case of possible mass exposure.

The Costa Luminosa isolated 1,427 passengers in their rooms on Sunday afternoon en route to Marseille, France from Fort Lauderdale, Fla. Over the past few days, one recent passenger with the infection died, two others were found to have it and three more suspected of having it have been removed from the ship.

One of the infected passengers was so ill that the ship called an ambulance to pick her up during a stop in Puerto Rico, on March 8. Samples from her and her husband were sent to the Centers for Disease Control and Prevention in Atlanta, delaying the diagnosis until this past Friday. Both were positive.

However, the ship, which is run by Carnival’s Italy-based Costa Cruises, did not increase sanitary protocols or begin testing temperatures until late Saturday afternoon, after receiving confirmation of the two cases from the Puerto Rican government.

“The protection of the health and safety of passengers and crew members is a top priority for Costa Cruises,” the line said in a statement, adding that sanitation levels had been “further raised in order to guarantee the maximum level of hygiene and safety for guests and crew.”

A series of cruise ships have had to confront exposures onboard, and four major lines have announced they would suspend departures from the United States for at least 30 days, allowing those currently at sea to continue. The question is where they will find a port.

The Costa Luminosa was turned away from Antigua and Spain. It is expected to arrive in France on Thursday, where all but the Italians are expected to disembark, and then head to a final stop in Savona, Italy.

Reporting was contributed by Mitch Smith, Mark Landler, Jonathan Weisman, Elisabetta Povoledo, Andrea Salcedo, Austin Ramzy, Tiffany May, Iliana Magra, Cliff Levy, Kristen Danis, Katrin Bennhold, Jason Gutierrez, Mariel Padilla, Robert Chiarito, Isabel Kershner, Mujib Mashal, Raphael Minder, Neil MacFarquhar, Jack Ewing, Najim Rahim, Livia Albeck-Ripka, Hannah Beech, Marc Santora, Julie Bosman, Richard Fausset, Johanna Berendt, Richard C. Paddock, Muktita Suhartono, Elian Peltier, Damien Cave, Javier Hernandez, Zolan Kanno-Youngs, Mihir Zaveri, Patricia Mazzei, Frances Robles, Badra Sharma, Annie Karni, Abdi Latif Dahir, Zach Montague, Claire Moses, Nina Siegal, Melissa Eddy, Vanessa Friedman, Vanessa Swales, Monica Davey and Thomas Fuller.

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