Most foreign nationals will not be allowed to enter the United States if they’ve been to China in the preceding two weeks.

[This briefing has ended. Read about the latest developments in the coronavirus outbreak here.]

Alex Azar, secretary of the United States Health and Human Services Department, announcing a travel ban on foreign nationals who have traveled to China, during a news conference at the White House on Friday.

The Trump administration is imposing temporary travel restrictions that bar entry into the United States by any foreign national who has traveled to China in the past 14 days, officials said Friday.

The restrictions, a reaction to the coronavirus that has been declared a public health emergency by the World Health Organization, will be put into place at 5 p.m. on Sunday. The United States on Friday also declared the coronavirus, which has sickened nearly 12,000 people and has spread to the United States and other countries, a public health emergency.

Friday’s action exempts immediate family members of American citizens and permanent residents.

In addition, officials said, any United States citizen returning home who has been in the Hubei province of China within the past 14 days will be quarantined for up to 14 days. Wuhan, the epicenter of the outbreak, is in Hubei.

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Those who have been to other parts of China within the past 14 days will be subject to “proactive entry screening” and up to 14 days of monitoring and self quarantine.

The United States will also funnel all flights from China to just a few airports, including Kennedy Airport, Chicago’s O’Hare and San Francisco International Airport.

The travel restrictions were announced Friday by Alex Azar, the secretary of health and human services, who declared that the coronavirus posed “a public health emergency in the United States.”

Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, said the actions were being taken because there were “a lot of unknowns” surrounding the virus and its transmission path.

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“The number of cases have steeply inclined with every day,” Dr. Fauci said.

Stocks sink again after airlines cancel flights to China.

Image A Delta Airlines aircraft at Shanghai Pudong International Airport in November. Credit... Alex Tai/SOPA Images/LightRocket, via Getty Images

The broadening outbreak has roiled stock markets and raised alarms about possible harm to global economic growth.

The S&P 500 suffered its sharpest decline of the year on Friday after major airlines in the United States said they would cancel flights to and from mainland China. It was the worst daily decline since October, and pushed the markets into negative territory for the year.

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The cancellations by Delta Air Lines, American Airlines and United Airlines were the latest example of economic disruption wrought by the coronavirus, just as the global economy had begun to recover from the trade war tensions that dominated 2019. Companies have restricted travel to the region, shut stores in China and warned of the possible financial impact.

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Economists seem certain that the travel shutdowns, factory closures and quarantines in mainland China will dampen economic activity there, but have said it is too soon to know the impact elsewhere.

“It is a wild card — I think even the experts would confirm that it’s too soon to tell,” said Richard Clarida, the vice chair of the Federal Reserve, during an interview on Friday on Bloomberg Television. The Fed is “monitoring closely,” he said.

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Concerns about global growth sent oil prices down below $52 a barrel. That pushed shares of energy companies down: Exxon Mobil and Chevron dropped by roughly 4 percent. Tech stocks also suffered, with particular weakness in the semiconductor sector, which is closely linked to supply chains based in and around China.

Economists have only begun to sketch out estimates on the potential effects of the outbreak. Many have taken comfort from the economic record of the SARS outbreak in China in 2002 and 2003, which suggests that any downturn might be limited in scope. SARS coincided with a relatively brief slowdown of global growth in early 2003, that was followed by a sharp rebound.

SARS, however, is an imperfect comparison. Some economists have suggested the ripple effects could be larger this time. At the time of the SARS outbreak, China represented just 5 percent of the global economy. In 2019, that number was 18 percent, according to JPMorgan economists.

Delta, United and American Airlines are suspending all flights between the U.S. and mainland China.

Image A traveler at an international terminal at Kennedy Airport in New York City, on Friday. Credit... Spencer Platt/Getty Images

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Delta Air Lines, United Airlines and American Airlines all said on Friday that they were suspending all service to mainland China as concerns about the coronavirus spread internationally.

American said it was suspending all flights to and from mainland China immediately through March 27. American and United will continue flights to Hong Kong.

Delta and United said they would suspend service starting on Feb. 6. United said it expected to resume operations on March 28.

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Delta, which does not fly to Hong Kong, said it would suspend service through April 30. Delta said in a statement that its last flight to mainland China from the United States would depart on Monday, and that its last flight to the United States from mainland China would leave on Wednesday.

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Delta was the first American airline to completely suspend service to China because of the virus. United Airlines had already reduced its service to the country this week.

Share prices in all three airlines had fallen by midday.

Airlines outside the United States are also clamping down on travel. In Rwanda and Kenya, RwandAir and Kenya Airways said they would cancel all flights to and from Guangzhou, the southern Chinese metropolis, until further notice. There have been no confirmed cases in Africa.

Poland’s national airline, LOT Polish Airlines, has suspended flights to China until Feb. 9, a deputy prime minister said on Twitter. More than a dozen people suspected of having the coronavirus are hospitalized in Poland, and over 500 people are being monitored by health services.

Iran has suspended all flights to China because of the coronavirus outbreak, according to Reuters. Iran’s semiofficial Tasnim news agency reported on Friday that all flights from China to the Islamic Republic have also been banned.

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Several Canadian companies have suspended employee travel to China after Air Canada’s decision on Wednesday to suspend service to Shanghai and Beijing. The Montreal-based carrier normally operates 33 flights a week to and from the two Chinese cities.

Americans evacuated from Wuhan are quarantined.

Image An aircraft transporting government employees and other Americans from Wuhan arrived at March Air Reserve Base in Riverside County, California, on Wednesday. Credit... Ringo H.W. Chiu/Associated Press

The United States government has imposed a federal quarantine on 195 people who were evacuated on Wednesday from Wuhan, China, to a California military base, officials said on Friday.

The group will be held at March Air Reserve Base in Riverside, Calif., for 14 days, to ensure that they are not infected with the coronavirus that has sickened more than 9,800 people in China and killed more than 200 people.

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More than 250 people have died, with nearly 12,000 infections confirmed.

Image Disinfecting a street in Wuhan on Thursday. Credit... Hector Retamal/Agence France-Presse — Getty Images

Chinese officials on Saturday reported the highest death toll so far in a 24-hour period.

◆ The 46 new deaths in China raised the toll to 259.

◆ About 2,100 new cases were also recorded in the country in the past 24 hours, raising the worldwide total to nearly 12,000, according to Chinese and World Health Organization data. The vast majority of the cases are inside China; about 100 cases have been confirmed in 21 other countries.

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◆ All of China’s provinces and territories have now been touched by the outbreak.

◆ Countries and territories that have confirmed cases: Thailand, Japan, Hong Kong, Singapore, Taiwan, Australia, Malaysia, Macau, Russia, France, the United States, South Korea, Germany, the United Arab Emirates, Canada, Britain, Vietnam, Italy, India, the Philippines, Nepal, Cambodia, Sri Lanka and Finland.

◆ Cases recorded in Thailand, Taiwan, Germany, Vietnam, Japan, France and the United States involved patients who had not been to China.

◆ No deaths have been reported outside China.

Fear of coronavirus comes to U.S. college campuses.

Image Students on the Arizona State University campus in Tempe, Arizona, on Thursday. Credit... Adriana Zehbrauskas for The New York Times

A call has been issued for classes to be canceled at Arizona State University. Basketball games were postponed at Miami University in Ohio. And at the University of Wisconsin-Platteville, two students from Wuhan were moved to a special dorm.

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On college campuses across the United States, the global alarm over coronavirus is particularly intense. Hundreds of students are being screened for the virus. Suspected cases at many colleges — Baylor, Wesleyan and Tennessee Tech — have turned out to be false alarms, but the anxiety continues.

At A.S.U., where there is one confirmed case of coronavirus, a cough in the back of a classroom now brings nervous glances. Students who had planned to study abroad this semester are furiously adjusting schedules.

Carolyn Kleve, 20, a junior at Arizona State who is 13 weeks pregnant, is afraid.

“We’re trapped in a room of 20 to 30 people and I don’t know who has what illness,” Ms. Kleve said of her classes. “Have I already come into contact with it? Who knows?”

A Chinese official feels ‘guilty and remorseful’ about the outbreak.

Image A mother and her son arriving at a checkpoint on the Yangtze River Bridge in Jiujiang, China, on Friday. Credit... Thomas Peter/Reuters

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A high-ranking Chinese official said on Friday that he felt responsible for the spread of the coronavirus, offering his most direct expression of responsibility for the crisis. Many residents and experts have said that the reluctance by the government in Wuhan to warn the public about the spreading disease created dangerous complacency.

“Above all, I feel guilty and remorseful and I reproach myself,” said Ma Guoqiang, the Communist Party secretary of Wuhan. “I’ve been constantly thinking that if I’d made the decision earlier to take the kind of strict controls we have in place now, the outcome would have been much better than now.”

Mr. Ma was asked about his feelings in an interview on China’s main television network, CCTV.

Wuhan’s mayor, Zhou Xianwang, who is less powerful than Mr. Ma, said the government’s own laws hindered faster public disclosure.

The State Department tells Americans not to travel to China.

Image Security personnel checking the temperatures of visitors entering Yuyuantan Park in Beijing, China on Friday. Credit... Tingshu Wang/Reuters

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The State Department on Thursday night issued a travel advisory telling Americans not to travel to China because of the public health threat posed by the dangerous new coronavirus. The department set the new advisory at Level 4, or red — its highest alert, reserved for the most perilous situations.

“Travelers should be prepared for travel restrictions to be put into effect with little or no advance notice,” the State Department said. “Commercial carriers have reduced or suspended routes to and from China.”

A spokeswoman for the Chinese foreign ministry, Hua Chunying, called the advisory an unfriendly act at a difficult time for China.

“True feeling shines through in hardship,” Ms. Hua said on Friday. “Many countries have shown their support and help for China’s fight against the epidemic. By contrast, the United States’ words and deeds are not in keeping with the facts and less are they in keeping with friendship.”

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The World Health Organization on Thursday declared the outbreak a global emergency after cases were discovered in more than a dozen countries.

Singapore and Mongolia will bar entries from China.

Image Lining up to buy masks at a mall in Singapore on Wednesday. The city-state has 13 confirmed cases of the coronavirus. Credit... Wallace Woon/EPA, via Shutterstock

Singapore on Friday announced a sweeping ban on Chinese visitors and other foreigners who had been to China in the past 14 days, in an escalation of travel restrictions by the Southeast Asian transportation hub.

The city-state will also stop issuing all forms of visas to people holding Chinese passports, Lawrence Wong, the minister for national development, said on Friday.

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Singapore has 13 confirmed cases of the coronavirus. The outbreak and the entry shutdown will be another blow to its economy, which was already hit by the fallout from the United States-China trade war.

Regional neighbors and airlines from countries that have not had any confirmed cases are also taking extra precautions to cope with the rapidly spreading epidemic.

The government of Mongolia said on Friday that it would close its border with China until March 2.

The authorities said they would work to bring home 30 Mongolian nationals from Wuhan, and its citizens in China would have until Feb. 6 to return. Non-Chinese foreigners visiting Mongolia will also not be able to enter through China.

Russia, which shares a 2,600-mile border with China, has also been racing to prevent the spread of the disease. The country reported its first two coronavirus cases on Friday, both in Siberia and among Chinese nationals who had recently traveled to China.

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Russia closed the border to pedestrians and cars on Thursday, and Deputy Prime Minister Tatyana A. Golikova said that Russia’s border with Mongolia would be closed to Chinese citizens. Russia will also temporarily stop issuing work visas to Chinese citizens, she added.

The first two confirmed cases are reported in Britain.

Image An ambulance leaving the Royal Air Force Brize Norton base in Carterton, England, on Friday. Credit... Adrian Dennis/Agence France-Presse — Getty Images

On Friday, Britain’s chief medical officer, Chris Whitty, said two residents had tested positive for coronavirus, the first known cases in the country.

In a statement, Mr. Whitty said the patients were members of the same family.

The announcement came as a flight carrying 83 British and 27 foreign nationals from Wuhan landed in Britain on Friday afternoon.

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The Britons were to be quarantined at Arrowe Park Hospital in Wirral, in northwest England, according to the BBC. The others will be flown on to Spain.

Italy declares an emergency, and Germany confirms a sixth case.

Image The Costa Smeralda cruise ship was docked in Civitavecchia, Italy, for more than 12 hours Thursday over concerns that someone aboard might have had the virus. Credit... Guglielmo Mangiapane/Reuters

The Italian government declared a six-month state of emergency on Friday after the first two cases of coronavirus were confirmed in Rome, according to a government official.

In a statement, the government said that it had allocated the “necessary funds” to begin precautionary measures. A government official said on Friday that five million euros, about $5.5 million, had been set aside for the effort.

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Two Chinese nationals, a husband and wife, were being held in isolation at Rome’s Spallanzani Hospital, which specializes in infectious diseases, after they tested positive for the virus.

The couple arrived in Milan a week ago and traveled to Parma and other cities before getting to Rome, where the husband began showing flu symptoms, the official said.

A group of Chinese tourists who had been traveling with the couple were also being held in isolation at the hospital, Italian officials said Friday.

At present, none of the other Chinese visitors showed any symptoms, said the Lazio region’s councilor for health, Alessio D’Amato, at a news conference on Friday.Three people who had come in contact with the infected couple were also being monitored at home, he also said.

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On Thursday, thousands of passengers had been blocked from leaving a cruise ship that docked at an Italian port for more than 12 hours over concerns that someone aboard might have had the virus. That episode was ultimately found to be a false alarm.

In Germany, the Bavarian state Health Ministry confirmed a sixth case of the virus on Friday — the first child to be infected in the country. The child is related to another coronavirus patient identified this week.

On Friday, a German passenger jet left for China to evacuate more than 100 German citizens from Wuhan and Hubei province, according to the German foreign ministry. Although none of the people on the passenger list appear to be infected, they will spend two weeks in quarantine once they arrive in Germany.

In a twist, China to evacuate Wuhan residents from foreign countries.

Image A shipment of protective suits arriving at Wuhan Tianhe International Airport on Thursday. Credit... Cheng Min/Xinhua, via Associated Press

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As foreign governments evacuated their citizens from China this week, China said it was arranging chartered flights to bring Wuhan residents who were overseas back to the epicenter of the outbreak.

Citing the “practical difficulties recently encountered” by residents abroad, the Ministry of Foreign Affairs said in a statement on Friday that evacuations would begin as soon as possible.

Five million people from Wuhan left the city last week before travel restrictions were enforced. Unnerved by the exodus, some regional countries and territories have banned entry to people from Wuhan or Hubei province.

Travel restrictions across China and the suspension of international flights to the country have left Chinese travelers stranded around the world.

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But it was unclear if the Chinese government was also targeting those who had intentionally fled the center of the outbreak. It was similarly unknown where the residents had traveled.

A mask heist occurs in Hong Kong amid a desperate shortage.

Image At a pharmacy in Hong Kong on Friday. Since the growing threat from the coronavirus became clear last week, Hong Kong residents have lined up outside pharmacies to buy masks. Credit... Jerome Favre/EPA, via Shutterstock

Someone stole 25,000 face masks from a warehouse in Hong Kong on Friday as the city, still haunted by memories of SARS, is struggling with a severe shortage.

The police said 500 boxes containing 50 masks each were reported missing from a building in an industrial neighborhood. The warehouse mostly supplied an e-commerce platform in the city, The Apple Daily newspaper reported.

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The theft came as residents in Hong Kong desperately searched for the item, often displayed at inflated prices, in pharmacies and retailers. In a dangerous practice, families that cannot afford new disposable masks have resorted to reusing them, according to local reports.

Reporting was contributed by Chris Buckley, Gerry Mullany, Elaine Yu, Li Yuan, E. Justin Swanson, Kate Conger, Miriam Jordan, Emma Bubola, Elisabetta Povoledo, Jason Horowitz, Geneva Abdul, Richard C. Paddock, Alex Marshall, Anton Troianovski, Joanna Berendt, Christopher Schuetze, Niraj Chokshi, Tariro Mzezewa, Mike Arnot, Denise Grady, Roni Caryn Rabin, Matt Phillips and Nicholas Bogel-Burroughs. Elsie Chen, Zoe Mou, Albee Zhang, Amber Wang, Yiwei Wang and Claire Fu contributed research.

Correction: Feb. 1, 2020 An earlier version of this briefing misidentified the Communist Party secretary of Wuhan, China. He is Ma Guoqiang, not Feng Guoqiang. Feb. 1, 2020

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