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BEIJING — Millions of Chinese had to cancel travel plans and hunker down in their homes to avoid exposure to a new, mysterious coronavirus Thursday as three cities in central China went on lockdown to curb the spread of the deadly virus that has already claimed 25 lives.

Health officials said that as of Thursday at least 835 cases of the coronavirus known as 2019-nCoV have been confirmed across China. New cases have also been popping up outside the country’s borders, including two in neighboring Hong Kong and one in Singapore on Thursday, as well as one in the U.S. earlier this week.

The number of deaths rose from 17 to 25, China Global Television Network reported Thursday night.

They are warning the virus could spread even further. Officials at the World Health Organization (WHO) are expected to hold a press conference later on Thursday to announce whether it can be classed as a global emergency.

People across China told NBC News the virus has disrupted their travel plans — just as the country is getting ready to celebrate the Lunar New Year, or Spring Festival, later this week, during which millions of people are expected travel both inside and outside China.

Speaking by phone from Shandong province in eastern China, university student Li Tianxin said her family has lost thousands of dollars after the virus forced them to cancel their travel plans.

“My family has prepared to go to Hainan [an island province of China] for the Spring Festival holiday, but worrying about the virus, we have to cancel all the flights and hotels,” the 21-year-old said.

Map: A deadly virus is spreading across the globe.

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Chinese health officials said Wednesday the new coronavirus can spread via respiratory transmission, heightening fears of a growing epidemic.

Many Chinese were stocking up on face masks and avoiding crowded places like cinemas and shopping centers.

“I couldn't find any mask on the market for sale. I dare not go outside," said college student Du Sijia, 21, from Xiamen on China’s southeast coast. "I don't even dare to order takeaways because I'm afraid of the virus."

A staff member checks the body temperature of a passenger after a train from Wuhan arrived in Hangzhou, China's eastern Zhejiang province, on Thursday. STR / AFP - Getty Images

Gao Duan, 27, who works at a drama company in Tianjin, northeastern China, said he is also staying at home for the time being.

“Every year we gather together to dine out for New Year Eve, but this year I asked my parents to cancel it,” Gao said.

In China’s capital, Beijing, bank clerk Zi Xian said he would normally enjoy going to temple fairs and watching movies during the Spring Festival holiday, “but now I would mostly remain indoors and avoid big crowds.”

The city of Wuhan in central Hubei province, the ground zero in China's fight against the new coronavirus, has been in quarantine. The virus is believed to have originated in one of its animal markets.

Wuhan is now closed off. No flights or trains out, and no mass transit within. Before dawn, we saw public buses parked on streets. A quarantine may seem a drastic move by #China's authorities but deemed crucial to contain the virus during the Lunar New Year travel rush. @NBCNews pic.twitter.com/hei8lS1Hjm — Janis Mackey Frayer (@janisfrayer) January 23, 2020

As of Thursday morning, roads, trains and flights into and out of the city, home to 11 million people, have been locked down.

Reuters reported that state media broadcast images of one of Wuhan's transport hubs, the Hankou rail station, nearly deserted, with gates blocked.

People walk past the closed Hankou Railway Station in Wuhan on Thursday after the city was locked down following the outbreak of a new coronavirus. China Daily / Reuters

Residents have also started buying food and daily items in bulk at local supermarkets as many families had to cancel their Chinese New Year dinner gatherings.

Meanwhile, authorities in Hong Kong stopped selling tickets for trains between the semi-autonomous territory and Wuhan Thursday, as two cases of the new coronavirus were confirmed there. They also called off some of the New Year celebrations in the city later this week.

Also on Thursday, Chinese authorities have enacted similar travel restrictions in two more cities neighboring Wuhan — Huanggang and Ezhou.

“I support the lockdown of Wuhan," former hotel manager Yi Yi, 55, said while on a walk in Beijing. "It shows China has the ability and experience to control this outbreak."

"We cancelled our plan to see our daughter", said Yi Yi in Beijing. Eric Baculinao / NBC News

Chinese government officials were criticized for their handling of the SARS epidemic that claimed the lives of nearly 800 people in 2002-2003, accused of downplaying the full extent of the outbreak, but have so far provided regular updates on the spread of the new coronavirus this week.

Yi, who is from Henan province north of Wuhan, said he too had his travel plans ruined by the outbreak.

“My wife and I originally planned to go to Melbourne, Australia to visit our daughter, but we cancelled the plans due to this virus,” he said. “As a Chinese saying goes, good work usually stays indoors while scandals travel a thousand miles, so with regards to the virus China had to do something to deal with international criticism.”

Eric Baculinao reported from Beijing, Yuliya Talmazan from London.