BEIJING — Chinese leader Xi Jinping warned Saturday the "accelerating spread" of coronavirus infections had created a "grave" situation in his populous nation, which extended travel restrictions to 48 million people in hardest-hit Hubei province, banned inter-province buses to Beijing and canceled tour group travel abroad.

As the Lunar New Year, China’s biggest holiday, began without much of the usual festivity, Hong Kong announced that schools would be closed through Feb. 17. The United States, France and Russia sought ways to evacuate their citizens from Wuhan, the central Chinese city of 11 million where the outbreak originated and is continuing to spread.

The pneumonia-like disease caused by a new coronavirus has killed at least 56 people and infected more than 1,900 in China, though conditions in Wuhan — where overcrowded hospitals are short of basic supplies — have led to speculation the outbreak may be far worse.

Two cases have been confirmed in the United States — one in Chicago and one outside Seattle, in travelers who have returned from Wuhan. Infections also have turned up in South Korea, Japan, Malaysia, Nepal, Thailand, Singapore, Vietnam, Taiwan, France and Australia.

Though the vast majority of illnesses and all the fatalities have been within China, growing concern about the disease has rippled across the globe. Governments outside China have continued to ramp up precautions.

Japan, expecting 400,000 Chinese tourists this week, advised staff at airports and shops to wear face masks while serving customers, something usually considered inappropriate for public-facing employees. Prime Minister Shinzo Abe said airlines arriving in Japan had been asked to distribute health surveys and advise customers to report symptoms, while checks had also been stepped up for people arriving by cruise ship.

In Granada, Spain, a tourist from Wuhan was isolated in a hospital after he showed up there with a fever, a Spanish media outlet reported. Other tourists in the group, who had no symptoms, were advised to remain in their hotel.

The International Olympic Committee moved a Summer Games qualifying event in boxing from Wuhan to Amman, Jordan. A women’s soccer qualifying match also planned for Wuhan has been shifted to Nanjing, China.

Facing the biggest public health challenge to the Chinese government in more than a decade, Xi instructed China’s highest ruling council, the Politburo Standing Committee, to “comprehensively mobilize” resources and manpower to provide medical aid, guarantee security and order in hospitals and provide markets with supplies in the cordoned-off city of Wuhan.

“As long as we are resolute . . . we can win the battle of controlling the epidemic,” he told top party leaders, according to state broadcaster CCTV.

Officials have announced the emergency construction of two hospitals to treat patients in Wuhan, where existing facilities are overflowing and medical personnel have been collapsing from exhaustion.

A study released Saturday suggested that each person with the virus is passing it to two or three others, which helps explain the rapid spread. The mathematical model from researchers at Imperial College London and the World Health Organization indicated that officials must stop more than 60 percent of the virus’s transmission to control the outbreak.

“It is uncertain at the current time whether it is possible to contain the continuing epidemic within China,” researchers wrote.

At U.S. airports, passengers arriving from China stood out because of the face masks almost all wore as protection against the virus. But they voiced varying levels of concern.

In Chicago, Sophia Shek, 42, of Hong Kong said life in her city over the last week has been “pandemonium.” Long lines snaked through stores to purchase supplies, and some retailers have taken advantage of the crisis by hiking prices to as much as $60 a mask, she said. Friends asked her to stock up and bring back face masks and other short supplies.

She said she is anxious about the virus and traveled only because the trip was for work. “I experienced SARS,” she said of the similar coronavirus that killed 774 people and infected more than 8,000, most of them in China, in 2002 and 2003. “This new virus is dormant so you don’t know if the person next to you has it.”

Bridget Russell, 55, a nurse from Austin, said the only extra precaution she noticed in Beijing was a sensor that checked passengers’ temperatures. The mood on her flight from the Chinese capital was calm, but she admitted, “it was freaky looking up and seeing 99 percent of the people wearing masks.” She joined them, wearing one on the flight and at O’Hare International Airport after she arrived.

At Los Angeles International Airport, Anthony Su, 53, who was on a flight from Taipei, Taiwan, to his home in Los Angeles after 10 days in Fuzhou, a city in southeastern China, said that when he first heard news of the outbreak, he stopped going out.

“I tried to avoid public areas, not go to the restaurant or any public place,” he said.

Others were more sanguine.

“We had SARS, so we are not that terrified,” said Eric Tsang, 40, of Hong Kong. “We have experience — masks on, wash your hands regularly, that’s okay for us.”

Tsang, visiting Los Angeles on business, said China has moved more quickly this time to quell the outbreak.

“China is doing better than before,” he said. “At least they acted very quickly. They asked to stop everybody, even during the holiday. I think this is a wise move.”

The spread of the virus was felt halfway around the world in Lunar New Year celebrations of the Year of the Rat in Chinese communities in the United States. At the University of Washington in Seattle, 30 minutes south of where the first U.S. case was confirmed, dozens of Chinese students turned out for the festivities — with some wearing face masks. They crowded into a residence hall lobby festooned with red paper lanterns, red tablecloths and garlands with the Chinese character for happiness.

Lindsey Gao, an 18-year-old freshman, said she was impressed by people who donned masks to protect themselves, but she didn’t think it was necessary.

“I admire them for doing that, but I think it looks a little weird,” said Gao, who emigrated from China when she was 6. Her mother, who lives on Mercer Island, across a floating bridge from Seattle, disagreed. “She texted me last night, ‘Did you buy a face mask?’ I said no, and she said, ‘Well, do you want to die?’ ”

A Chinese woman who declined to give her name said she had canceled her family’s restaurant reservations and would be having dinner at home. She doubted she’d be preparing a traditional Chinese feast; caution about the virus also kept her away from the Asian market to buy ingredients.

The Northwest Chinese School, with locations in Bellevue and Seattle, sent out an email calling off weekend classes. “We take the health of our students and families very seriously and think that this is the best course of action,” administrators wrote.

Kevin Ma, 28, a Seattle tutor, said he hasn’t detected any stigma or ethnic profiling of Chinese people. “I don’t think we’re there yet,” he said. “People are pretty sensitive to the fact that just because you are Chinese doesn’t mean you have it.”

Denyer reported from Tokyo, and Abutaleb and Bernstein reported from Washington. Shibani Mahtani in Hong Kong, Bonnie Rochman in Seattle, Mark Guarino in Chicago, Miranda Green in Los Angeles and Brian Murphy in Washington contributed to this report.