Travelers wear face masks as they stand in the arrivals area at Beijing Capital International Airport in Beijing, Thursday, Jan. 23, 2020. China closed off a city of more than 11 million people Thursday, halting transportation and warning against public gatherings, to try to stop the spread of a deadly new virus that has sickened hundreds and spread to other cities and countries in the Lunar New Year travel rush. (AP Photo/Mark Schiefelbein)

BEIJING (AP) — China decided today to lock down three cities that are home to more than 18 million people in an unprecedented effort to try to contain a deadly new viral illness that has sickened hundreds and spread to other cities and countries in the Lunar New Year travel rush.

Police, SWAT teams and paramilitary troops guarded Wuhan’s train station, where metal barriers blocked the entrances at 10 a.m. sharp. Only travelers holding tickets for the last trains were allowed to enter, with those booked for later trains being turned away.

Normally bustling streets, shopping malls, restaurants and other public spaces in the city of 11 million people were eerily quiet. In addition to the train station, airport, ferry, subway and bus services were also halted.

Similar measures will take effect from Friday in the nearby cities of Huanggang and Ezhou. Theaters, internet cafes and other entertainment centers were also ordered closed, further increasing the economic costs of the response to the outbreak.

“To my knowledge, trying to contain a city of 11 million people is new to science,” Gauden Galea, the World Health Organization’s representative in China, told The Associated Press in an interview at the WHO’s Beijing office. “It has not been tried before as a public health measure. We cannot at this stage say it will or it will not work.”

The illnesses from a newly identified coronavirus first appeared last month in Wuhan, an industrial and transportation hub in central China’s Hubei province. The vast majority of mainland China’s 571 cases have been in the city.

Other cases have been reported in the United States, Japan, South Korea and Thailand. One case was confirmed today in Hong Kong after one was earlier confirmed in Macao. Most cases outside China were people from Wuhan or who had recently traveled there.

A total of 17 people have died, all of them in and around Wuhan. Their average age was 73, with the oldest 89 and the youngest 48.

Images obtained from inside Wuhan following the closure showed long lines and empty shelves at supermarkets, as residents stocked up for what could be weeks of relative isolation. That appeared to be an over-reaction, since no restrictions have been placed on trucks carrying supplies into the city, although many Chinese still have strong memories of shortages and privations in the years before the country’s recent economic boom.

Such sweeping measures are typical of China’s authoritarian communist government, although their effectiveness in containing the outbreak remains uncertain.

Local authorities in Wuhan have demanded all residents wear masks in public places and urged government staff to wear them at work and for shopkeepers to post signs for their visitors, Xinhua news agency quoted a government notice as saying.

Xinhua cited the city’s anti-virus task force as saying the measures were taken in an attempt to “effectively cut off the virus spread, resolutely curb the outbreak and guarantee the people’s health and safety.”

Liu Haihan left Wuhan last Friday after visiting her boyfriend there. She said everything was normal then, before human-to-human transmission of the virus was confirmed. But things have changed rapidly.