Announcing this at a press conference, Chief Executive Carrie Lam Cheng Yuet-ngor also said the city will cancel its largest marathon to help with disease control efforts.

The Standard Chartered Hong Kong Marathon, originally scheduled for Feb 8 and 9, involves 70,000 people and the government “believes it has to be canceled,” Lam said.

Lam said Hong Kong will also indefinitely halt flights and rail services to Wuhan in central China’s Hubei province where the novel coronavirus outbreak started.

The government said those who arrive in Hong Kong via the international airport, the three ports and six immigration checkpoints at the city’s border with Shenzhen, will be required to declare their health conditions in special forms. Those who provide fake information will be liable to attract up to six months’ imprisonment and a fine of HK$5,000.

The CE will lead a steering committee to address the threat and said that the government will spare no efforts or resources in preventing a community outbreak of the disease.

The government will set up four task forces, designated for disease prevention and control, internal coordination, public participation and public information, respectively.

Lam said the date for all secondary schools, elementary schools and kindergartens to start a new semester will be pushed back to Feb 17.

Lam urged Hong Kong people not to visit Hubei province. She said she has called on the State Council for help to keep the city’s mask stockpile adequate. Pharmacies across Hong Kong have run out of masks aimed at preventing viral infection, prompting authorities to say more will arrive next week.

The majority of confirmed cases – which has climbed to over 1,200 in the Chinese mainland – have been in older people and those with underlying health conditions, but health experts have said that children and teenagers also should take precautions against the virus.

According to local health authorities in Guangxi, the infected minor lives in Wuhan, Hubei province – the epicenter of the outbreak. She flew to Nanning, the provincial capital of Guangxi, from Wuhan on Tuesday and then rode a bus to Hechi city, about 250 kilometers north of Nanning.

She visited a local hospital in the early hours on Thursday after showing symptoms of fever and a cough. The girl is now being quarantined for treatment and is in stable condition, local health authorities said.

Previously, South China’s Guangdong province also confirmed infection in young children.

A 10-year-old boy who returned from Wuhan to Guangdong’s Shenzhen city on Jan 4 was hospitalized on Jan 11 and later confirmed to have contracted the virus, local newspaper Guangzhou Daily reported.

The boy is reportedly cured of the illness and was discharged from the hospital on Thursday.

Li Lanjuan, a member of the high-level expert team convened by the National Health Commission, said on Thursday that the elderly population and those with chronic diseases or low immunity levels are more vulnerable to the novel coronavirus, but children and teenagers are not immune to the virus and should take proper protective measures.

The pneumonia-like disease has claimed 41 lives – all in China – and infected more than 1,200 people there. An official at the World Health Organization told reporters that his agency has begun planning for an outbreak that will last for months.

Infections have been confirmed in France, South Korea, Japan, Nepal, Thailand, Singapore, Vietnam, Taiwan,Australia and the United States as the disease spreads outside Asia.

At least 50 people are under observation for the illness in 22 U.S. states, according to the Centers for Disease Control and Prevention.

The second U.S. patient is a woman, a Chicago resident, who traveled to Wuhan, China – where the virus originated – in late December and returned Jan. 13, the CDC announced Friday. A few days later, she began to feel ill and saw a doctor. She was asked about her travel history, then referred to a hospital, which isolated her and arranged for testing.

The woman is in stable condition but will remain in the hospital mainly to ensure she does not spread the virus. On Tuesday, authorities revealed the first U.S. case, a man in his 30s from Snohomish County, Washington, who had recently returned from a visit to Wuhan. Authorities said they are monitoring 50 of the man’s contacts for signs of infection.

The CDC deployed a team to help with the Chicago case. The woman “has not had any extended close contact with anyone outside her home since returning, and that should be very reassuring to the public,” Allison Arwady, Chicago’s public health commissioner, told reporters Friday.

Health officials briefed about two dozen senators Friday. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said he “wouldn’t be surprised if there are additional cases.” But he said public-health authorities acted quickly in Illinois, where they “identified, isolated and did contact tracing on the people with whom that person came into contact. That’s how you get your handle on an outbreak.”

After the briefing, Sen. Rick Scott, R-Fla., called on President Donald Trump to declare the outbreak a public-health emergency.

Although the outbreak is a “very serious public-health threat, the immediate risk to the U.S. public is low at this time,” Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, told reporters in a briefing Friday.

Circumstances in the United States were overshadowed by the apparently deteriorating conditions in China. The Chinese medical system is struggling to cope with the outbreak, amid reports of overcrowded hospitals, stressed doctors and dwindling supplies.

A doctor who had been working on the front line of efforts to control the disease in Wuhan died on Saturday, Chinese state media reported.

Liang Wudong was 62 and had retired a year ago, according to staff at Hubei Xinhua hospital, but was apparently called back to work to help combat the disease. He fell ill with suspected coronavirus on Jan. 16 before being transferred to another hospital in the city as a patient.

A ban on travel was extended to 14 cities, with a total population of more than 35 million in central China’s Hubei province. Tunnels under the Yangtze River were blocked to stop the flow of traffic, and all ride-hailing services in Wuhan were halted at midday Friday. Only half the city’s taxis are allowed on the road each day.

China Southern, the country’s biggest airline, had already canceled flights in and out of Wuhan airport on Thursday. The other two main carriers, Air China and China Eastern, said they would cancel all Wuhan flights from Friday until at least Feb. 8.

As the Lunar New Year began, authorities have canceled the temple fairs and festivals that normally accompany the nation’s biggest holiday. Large public gatherings could aid the spread of the airborne virus.

Nevertheless, state broadcaster CCTV led its midday news program with a report about a huge banquet in Beijing attended by President Xi Jinping and other Communist Party leaders. None of them was wearing a mask, and the report made no mention of the virus outbreak.

Other senior Chinese officials came under heavy criticism for their slow response to the outbreak. The mayor of Wuhan, Zhou Xianwang, allowed a huge potluck banquet to proceed Sunday, during a weekend when the number of confirmed infections shot up dramatically. The city had arranged a Lunar New Year meal featuring 14,000 dishes for more than 40,000 people, an event it hoped to get listed in Guinness World Records.

Residents were also surprised by photos and video of the two top officials in Hubei province – the Communist Party secretary and the governor – at a dance performance in Wuhan to celebrate the arrival of the Spring Festival holiday. They were sharply criticized for enjoying themselves instead of working on the response to the health crisis.

The Forbidden City in Beijing, which can admit 80,000 people a day and was entirely sold out for the holiday, has been closed until further notice. Shanghai Disneyland, which normally has 10 million visitors a year, announced Friday that it would shut down indefinitely starting Saturday.

Production companies have postponed the release of seven films over the holiday, prompting Chinese cinema companies to close the country’s 70,000 movie theaters.

Schools in Hubei province, due to begin the spring semester after the holiday, will not open their doors as planned but will wait for further guidance from health authorities. The Education Ministry instructed universities around China to delay their opening dates if necessary.

Workers are racing to build a 1,000-bed hospital for people with the disease in Wuhan, an indication that Chinese officials expect, or already have, a much larger number of cases. It is modeled after a medical facility specially built in 2003 for patients with SARS, another respiratory infection that began in China and claimed more than 750 lives in more than a dozen countries. The new virus is closely related to the SARS coronavirus.

China’s state-run Xinhua News Agency said the new hospital is needed “to address the insufficiency of existing medical resources.”

One of the most recent fatalities was a young, previously healthy man in Wuhan, raising concerns about the deadliness of the virus. He had no chronic diseases or other existing health conditions, and had been treated with anti-viral medication and antibiotics since he was admitted to a hospital on Jan. 9.

Until now, the vast majority of victims have been older than 60 with underlying health conditions.

Aside from 1,287 confirmed cases of infection, a total of 8,420 people are reported to be under observation in China.

Despite the escalating toll, some analysts remained concerned that the Chinese government was significantly underreporting the number of cases. A financial analyst for the investment firm Raymond James told clients in a report Thursday night that he believes the numbers are likely at least 10 times the publicly reported total.

With transportation restrictions imposed by China, U.S. officials said Friday they are assessing the extent and duration of screening travelers from Wuhan to airports in San Francisco, Los Angeles, New York, Atlanta and Chicago. The lockdown in Wuhan and nearby cities means fewer travelers from there are arriving in the United States.

The labor-intensive airport screening is being conducted by the CDC. But sick patients with no symptoms might not be detected.

To control the spread of the virus, resources must be focused at the state and local levels, where front-line health officials are trying to rapidly identify cases, said Martin Cetron, director of the CDC’s division of global migration and quarantine.

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Sun, O’Grady and Bernstein reported from Washington. The Washington Post’s Lyric Li and Yuan Wang in Beijing, Simon Denyer in Tokyo, and Yasmeen Abutaleb, Jason Aldag and Miriam Berger in Washington contributed to this report.