BEIJING — The Chinese government struggled Sunday to cope with a worsening coronavirus epidemic as its official number of infections soared 50 percent in one day and additional cases appeared in the United States.

The government in Beijing broadened an extraordinary quarantine to more than 50 million people — roughly equal to the population of Spain — enforcing a travel ban on 16 cities in central Hubei province, where the lethal virus first appeared.

In the U.S., health officials confirmed three new cases — one in Arizona and two in California — bringing the total to five. The patients — in Southern California, Chicago, Arizona and Washington state — had traveled from Wuhan, officials with the Centers for Disease Control and Prevention said. All are hospitalized.

As of midafternoon Sunday, the CDC has been investigating 100 people in 26 states, including the five who were confirmed infected. Of those, 25 people have been tested and are not infected with the virus.

Health officials expect more American cases, Nancy Messonnier, director CDC’s National Center for Immunization and Respiratory Disease, told reporters. But the virus is not believed to be spreading from person to person in the U.S., she said.

“For this reason, we continue to believe that the immediate health risks from the 2019 coronavirus to the general American public is low at this time,” Messonnier said. “But the threat is serious, and our public health response is aggressive, with the aim of helping protect Americans.”

Chinese officials, however, say the worst is yet to come. Health Minister Ma Xiaowei said Sunday that the virus is developing the ability to spread more easily, while the vice minister of industry, Wang Jiangping, said demand for medical supplies is overwhelming China’s ability to produce them.

The mayor of Wuhan, the epicenter of the outbreak, said he expects at least 1,000 more infections to surface. Workers are racing to build at least three pop-up 1,000-bed hospitals in the city to cope with the anticipated surge.

Patients also have been confirmed in France, South Korea, Japan, Nepal, Thailand, Singapore, Vietnam, Taiwan and Australia.

After a slow start, Chinese authorities have moved aggressively to combat the novel ailment. Officials indefinitely extended the annual Lunar New Year holiday beyond its scheduled Jan. 30 end and deployed more than 1,000 doctors and military personnel to Wuhan.

The State Department, meanwhile, plans to evacuate diplomats posted at the U.S. Consulate in Wuhan on a charter flight on Tuesday, according to a statement posted on the website of the U.S. Embassy in Beijing. The consulate is roughly two miles from the Huanan Seafood Market, where the virus is believed to have first jumped from wild animals to humans.

A “limited” number of seats on the aircraft will be available for other Americans seeking to flee the city, with priority being given to those most at risk of succumbing to the fatal illness, the statement said.

Chinese authorities have banned the sale of wild animals for the duration of the crisis.

The economic fallout from the epidemic also is likely to be significant. Even before the outbreak, China’s economy was slowing, hampered by the trade war with the United States and government efforts to trim an addiction to borrowing. The galloping virus, which has crimped travel, shuttered movie theaters and idled factories, will further depress growth.

That will put pressure on Chinese officials to pause their debt-reduction campaign and goose the economy with more spending. Federal Reserve Chair Jerome H. Powell may address the implications for the global economy at Wednesday’s scheduled meeting of the central bank’s rate-setting committee, said Diane Swonk, chief economist for Grant Thornton in Chicago.

The virus will also imperil China’s ability to meet the targets for additional purchases of U.S. goods contained in the trade deal President Trump signed earlier this month.

That “phase one” accord calls for China over the next two years to buy $200 billion worth of American goods and services beyond previous levels, a goal many analysts regarded as ambitious even before the outbreak of disease.

“All of a sudden phase one looks pretty hard to reach,” said Swonk.

China’s health minister, Ma Xiaowei, told reporters Sunday that the virus is infectious during its incubation period, meaning that a person could spread it to others before experiencing symptoms. That’s a significant difference from the SARS (severe acute respiratory syndrome) coronavirus, which began in China in 2002 and spread globally, killing 774 people.

The Chinese announcement about the new coronavirus’s transmissibility could explain the soaring rate of infection in China, which registered a 50 percent jump in cases on Sunday. Local authorities expect a similar leap on Monday.

But the CDC does not have “any clear evidence of patients being infectious before symptom onset,” Messonnier said during the Sunday news conference, adding that health officials are “actively investigating” that possibility.

China’s national health commission reported that 1,975 people across 30 provinces had been infected as of Sunday. Fifty-six deaths have been reported, including in major metropolitan areas such as Shanghai. Several doctors in Beijing, the capital, also reported being infected.

Scientists say the virus is adapting to humans much faster than SARS. It took the SARS virus three months to mutate into a form that spread easily among humans, but the related Wuhan coronavirus took only one month, George Fu, a top Chinese epidemiologist, told reporters.

“Why is it transmitting so fast?” he said. “The two species are like the cartoon Tom and Jerry: Viruses are continually adapting to humans, but human also adapt, and the virus’s ability to make people ill also goes down.”

The director-general of the World Health Organization (WHO) said he was en route to Beijing for meetings with Chinese government officials. Tedros Adhanom Ghebreyesus, named to the post in 2017, said on Twitter that the agency was “working 24/7 to support” Chinese efforts to battle the disease.

The Wuhan coronavirus has caused mild to severe respiratory illness, fever, coughing and shortness of breath. The CDC believes symptoms can manifest two to 14 days after exposure. At this time, no drugs or vaccines have been recommended specifically to treat the virus.

At the heart of the outbreak, in central China’s Hubei province, a travel ban extended to a total of 16 cities and covered about 51 million people. Video distributed by state media showed local officials in adjacent regions taking extreme measures, including using excavators to destroy and block roads, to discourage residents from traveling to infected areas of Hubei to visit stranded relativesinside the quarantine zone.

China’s Center for Disease Control on Sunday found large amounts of the coronavirus from samples taken from Wuhan’s South China seafood market, where wild animals, including deer and bats, were being sold.

“It is highly suspected that the epidemic is related to wildlife trade,” state broadcaster CCTV reported. Researchers say the related SARS coronavirus in 2002 probably originated in bats and spread to humans through the civet cat, which was sold in wildlife markets and eaten as a delicacy in southern China.

The spread of the virus — and travel bans extending to several major hubs in China — threatened to paralyze the country for an indefinite period. Officials in Beijing said Sunday that they “have not and will not close the city because of the epidemic” in response to online rumors suggesting an imminent lockdown of the capital, which has a population of 22 million, with a significant fraction traveling this week to visit family.

Two teams of British epidemiologists released studies over the weekend estimating that each infected person was spreading the disease to two or three people. A team from Lancaster University projected that infections in Wuhan could explode to 190,000 cases by as early as next week.

Worshipers wear masks to prevent an outbreak of a new coronavirus as they make offerings of incense sticks during a Lunar New Year celebration at Che Kung Temple in Hong Kong Jan. 26, 2020. (Tyrone Siu/Reuters)
Worshipers wear masks to prevent an outbreak of a new coronavirus as they make offerings of incense sticks during a Lunar New Year celebration at Che Kung Temple in Hong Kong Jan. 26, 2020. (Tyrone Siu/Reuters)

The Chinese central government said it is mustering manufacturers to send 100,000 hazardous-materials suits and millions of face masks to Wuhan, where hospitals reported overfilled beds and doctors collapsing from exhaustion. Videos on social media from Wuhan hospitals showed patient queues stretching around the block and nurses worrying the true number of cases — based on what they were witnessing — far exceeded what was being officially reported.

The vice minister of industry, Wang Jiangping, said Sunday that the country was facing a significant shortage of medical supplies, including protective suits for medical workers. Hubei province alone required 100,000 suits a day, he said, but Chinese manufacturers could only produce 30,000 a day.

Michael Einhorn, president of Dealmed, an independent medical supply distributor in New York, New Jersey, Connecticut and Pennsylvania, said prices of masks jumped as soon as news of the virus spread, while sales volumes tripled through retailers such as Amazon.

Dealmed typically carries at least 90 days’ supply but currently has only about two weeks’ worth left.

If demand continues, the availability of masks will be “very limited” within 10 days, Einhorn said in a statement, and if the virus continues to spread, there will be “extreme shortages” in as early as three weeks’ time.

Workers from local disease control and prevention department in protective suits disinfect a residential area in Ruichang, Jiangxi province, on Jan. 25, 2020. (Reuters)
Workers from local disease control and prevention department in protective suits disinfect a residential area in Ruichang, Jiangxi province, on Jan. 25, 2020. (Reuters)

Meanwhile, Chinese citizens stranded inside the vast quarantine zone, locked down by paramilitary police checkpoints for the fourth day, took to social media to describe a sense of surreal desperation during a week when families should be celebrating the new year with dumplings, fireworks and presents.

One Wuhan resident described sharing the dwindling groceries she had purchased to last for three days with an elderly couple whose food supplies were exhausted.

“I don’t know how to solve this food problem,” wrote the user, Guapidawushi. “Right now I really, really don’t know what to do. I’m completely helpless.”

Some users shared videos of once-buzzing streets in Wuhan’s historic, European-style riverside district lying empty. Others posted more lighthearted pictures of women playing Mah-jongg with masks and transparent grocery bags over their heads.

The situation appeared to be more dire in the vast Hubei countryside.

The Chinese magazine Caijing reported that some smaller village clinics were rationed only six masks, and large hospitals were within one or two days of running out of supplies. In Jingzhou city, a short distance up the Yangtze River from Wuhan, doctors told reporters that they were wearing rain ponchos because they lacked protective suits.

In Hong Kong, where a sixth case of the virus was confirmed Sunday, pressure is mounting on the government to tighten border controls with China. One hospital workers’ union threatened a five-day strike if more measures weren’t taken.

Protesters in the evening attacked a building that has been set aside for quarantine and set its lobby alight with molotov cocktails, police reported.

“We are all nervous here and everyone has begun curtailing their social lives,” said Andrew Collier, managing director at Orient Capital Research. “I was planning a trip to China but will delay that until there is more information.”

Denyer reported from Tokyo. Lynch and Shammas reported from Washington. Min Joo Kim in Seoul, Shibani Mahtani in Hong Kong, Lyric Li in Beijing, Paul Schemm in Dubai contributed to this report.