BEIJING — A Chinese city of more than 11 million people planned to shut down outbound flights and trains Thursday as the world’s most populous country battled the spread of a new virus that has sickened hundreds of people and killed 17, state media reported.

Everyone in the city of Wuhan was to be restricted to some degree. The stateowned People’s Daily newspaper said no one would be allowed to leave. The official Xinhua News Agency said no one could leave without a specific reason.

Train stations and the airport were to shut down at 10 a.m. Buses, subways, ferries and long-distance shuttle buses would also be temporarily closed.

Most of the cases are in Wuhan and surrounding Hubei province, but dozens of infections have popped up this week around the country as millions travel for the Lunar New Year, one of the world’s largest annual migrations of people. A handful of infected people who came from Wuhan have also been found overseas.

In Geneva, the World Health Organization put off deciding whether to declare the outbreak a global health emergency and asked an expert committee to continue meeting for a second day Thursday.

“We need more information,”

WHO Director-General Tedros Adhanom Ghebreyesus said.

WHO defines a global emergency as an “extraordinary event” that constitutes a risk to other countries and requires a coordinated international response.

When asked about Wuhan’s public transport shutdown, WHO chief Tedros said authorities were likely acting to prevent transmission and mass gatherings.

“We cannot say they have done something unusual,” he said.

The number of new cases has risen sharply in China, the center of the outbreak.

The 17 deaths were all in Hubei province, where the outbreak emerged in the provincial capital of Wuhan late last month. Wuhan authorities said the province has confirmed 444 cases, which would bring the national total to more than 500.

The illness comes from a newly identified type of coronavirus, a family of viruses that can cause the common cold as well as more serious illnesses, such as the SARS outbreak that spread from China to more than a dozen countries in 2002-2003 and killed about 800 people. Some experts have drawn parallels between the new coronavirus and Middle Eastern respiratory syndrome, another coronavirus that does not spread easily among humans and is thought to be carried by camels.

“There has already been human-to-human transmission and infection of medical workers,” Li Bin, deputy director of the National Health Commission, said at a news conference Wednesday. “Evidence has shown that the disease has been transmitted through the respiratory tract, and there is the possibility of viral mutation.”

A tweet from WHO’s Asia office this week raised the possibility that the epidemic is spreading more easily and may no longer require an animal source to spark infections, as officials initially reported.

Authorities in Thailand on Wednesday confirmed four cases – a Thai national and three Chinese visitors. Japan, South Korea, the United States, Taiwan and Macao, a former Portuguese colony that is a semi-autonomous Chinese city, have all reported one case each.

All of the illnesses were of people from Wuhan or who recently traveled there.

In response to the U.S. case, President Trump said: “We do have a plan, and we think it’s going to be handled very well.” He said the U.S. and China were both “in very good shape.”

The patient, a man in his 30s who traveled to China in November, was doing well in an isolation unit in a hospital north of Seattle. He returned to Washington state Jan. 15, before the start of U.S. airport screening, health officials said.

In Wuhan, pharmacies limited sales of face masks to one package per customer as people lined up to buy them.

Medical workers in protective suits could be seen carrying supplies and stretchers into Wuhan Medical Treatment Center, where some of the patients are being treated.

Officials said it was too early to compare the new virus with SARS or MERS, or Middle East respiratory syndrome, in terms of how lethal it might be. They attributed the spike in new cases to improvements in detection and monitoring.