Health officials fear of hike in the transmission rate as hundreds of millions of Chinese travel at home and abroad during week-long holidays for the Lunar New Year, which begins on Saturday.
The previously unknown virus strain is believed to have emerged late last year from illegally traded wildlife at an animal market in the central Chinese city of Wuhan. Most transport in Wuhan, a city of 11 million people, was suspended on Thursday morning and people were told not to leave. Hours later, state media in neighbouring Huanggang, a city of some 6 million people, said it was imposing a likely lockdown.
However, Chinese authorities have not given any new details on the numbers of virus infections but it has been reported in Beijing, Shanghai, Hong Kong, and several other countries including the United States, alarming fears it is already spreading worldwide.
Wuhan's city government said it would shut down all urban transport networks and suspend outgoing flights from 10 am. According to domestic media, some airlines were operating after the deadline. State media broadcast images of one of Wuhan's transport hubs, the Hankou rail station, almost vacant, with gates locked. The government is requesting citizens not to leave the city.
State media reported highway toll booths around Wuhan were closing down, which would effectively cut off road exits. One resident told news agency, guards were patrolling major highways. As the city gets alieneated, residents rushed into hospitals for check-ups and scrambled for supplies, clearing out supermarket shelves and lining up for petrol.
Authorities in Huanggang ordered indoor entertainment venues including cinemas and internet cafes to remain close and were asking citizens not to leave other than under special circumstances, said state media.
China's National Health Commission had confirmed 571 cases and 17 deaths by the end of Wednesday. Earlier, it said another 393 suspected cases had been reported. Out of eight known cases worldwide, Thailand has confirmed four, while Japan, South Korea, Taiwan and the United States have reported one each.
In a report on Wednesday, Imperial College London said it estimated a total of 4,000 cases of the coronavirus in Wuhan alone as of January 18, an infection rate based on the number of cases reported in China and elsewhere.
The World Health Organization (WHO) has said it will decide on Thursday whether to declare the outbreak a global health emergency, which would step up the international response. If it does so, it will be the sixth international public health emergency to be declared in the last decade.
Some experts believe the new virus is not as dangerous as previous coronaviruses such as SARS and Middle East Respiratory Syndrome (MERS), which has killed more than 700 people since 2012.
"The early evidence at this stage would suggest it's not as severe," Australia's Chief Medical Officer Brendan Murphy told reporters.
WHO Director-General Tedros Adhanom Ghebreyesus told reporters in Geneva that China's actions were "very strong" but called on it to take "more and significant measures to limit or minimise the international spread".
"We stressed to them that by having a strong action not only they will control the outbreak in their country but they will also minimise the chances of this outbreak spreading internationally. So they recognise that," he said.
Despite China's response, stock markets across Asia were on the back foot on Thursday, led by drops of roughly 1.5% in Hong Kong and Shanghai while China's yuan fell to a two-week low.