BEIJING — China has moved to lock down at least three cities with a combined population of more than 18 million in an unprecedented effort to contain the deadly new virus that has sickened hundreds of people and spread to other parts of the world during the busy Lunar New Year holiday.

The open-ended lockdowns are unmatched in size, embracing more people than New York City, Los Angeles and Chicago put together.

The train station and airport in Wuhan, the epicenter of the outbreak, were shut down, and ferry, subway and bus service was halted. Normally bustling streets, shopping malls, restaurants and other public spaces in the city of 11 million were eerily quiet. Police checked all incoming vehicles but did not close off the roads.

Similar measures were being imposed today in the nearby cities of Huanggang and Ezhou. In Huanggang, theaters, internet cafes and other entertainment centers were also ordered closed.

In the capital, Beijing, major events were canceled indefinitely, including traditional temple fairs that are a staple of holiday celebrations, to stop the spread of the virus. The Forbidden City, the palace complex in Beijing that is now a museum, announced it will close indefinitely on Saturday.

China’s National Health Commission said this morning the confirmed cases of the new coronavirus had risen to 830 with 25 deaths. The first death was also confirmed outside the central province of Hubei, where the capital, Wuhan, has been the epicenter of the outbreak. The health commission in Hebei, a northern province bordering Beijing, said an 80-year-old man died after returning from a two-month stay in Wuhan to see relatives.

The vast majority of cases have been in and around Wuhan or people with connections the city. Other cases have been confirmed in the United States, Japan, Taiwan, South Korea and Thailand. Singapore and Vietnam reported their first cases Thursday, and cases have also been confirmed in the Chinese territories of Hong Kong and Macao.

Many countries are screening travelers from China for symptoms of the virus, which can cause fever, coughing, breathing difficulties and pneumonia.

The World Health Organization has decided against declaring the outbreak a global emergency, a step that can bring more money and resources to fight a threat but that can also cause trade and travel restrictions and other economic damage, making the decision a politically fraught one.

The decision “should not be taken as a sign that WHO does not think the situation is serious or that we’re not taking it seriously. Nothing could be further from the truth,” WHO Director General Tedros Adhanom Ghebreyesus said. “WHO is following this outbreak every minute of every day.”

Chinese officials have not said how long the shutdowns of the cities will last. While sweeping measures are typical of China’s Communist Party-led government, large-scale quarantines are rare around the world, even in deadly epidemics, because of concerns about infringing on people’s liberties. And the effectiveness of such measures is unclear.

“To my knowledge, trying to contain a city of 11 million people is new to science,” said Gauden Galea, the WHO”s representative in China. “It has not been tried before as a public health measure. We cannot at this stage say it will or it will not work.”

Jonathan Ball, a professor of virology at molecular virology at the University of Nottingham in Britain, said the lockdowns appear to be justified scientifically.

“Until there’s a better understanding of what the situation is, I think it’s not an unreasonable thing to do,” he said. “Anything that limits people’s travels during an outbreak would obviously work.”