- Video report by ITV News Asia Correspondent Debi Edward
No one is to be allowed to leave Wuhan - the city at the centre of the coronavirus outbreak - in a bid to stop the potentially deadly disease from spreading.
Chinese state media reported the lockdown will begin at 10am on Thursday morning when a travel ban comes into force.
All public transport in the city, plus flights and trains departing it will be cancelled.
Coronavirus originated at a seafood and illegal animal market in Wuhan last month.
Seventeen people have now died from the illness and more than 541 have been infected, with cases detected in countries including the US, Japan, South Korea, Macao and Taiwan.
On Thursday, the World Health Organisation (WHO) is expected to make a decision on whether or not to declare an international public health emergency.
It had been anticipated that a decision would be made on Wednesday, but WHO director-general Tedros Adhanom Ghebreysus said the organisation needed more information before deciding what to do, describing it as an "evolving and complex situation".
- What do the experts know about the coronavirus?
As well as the travel ban, the Wuhan government has ordered everyone in the city to wear a mask in public, as efforts are stepped up to prevent the disease from spreading .
The travel ban comes ahead of the Lunar New Year holiday rush, when millions of Chinese travel at home and abroad in the biggest human migration.
While there have been no cases of coronavirus in the UK, Heathrow Airport separated passengers arriving on Wednesday's direct flight from Wuhan.
Passengers were not tested for signs of illness when they disembarked, but they were handed information leaflets from Public Health England (PHE) about what they should do if they began developing symptoms.
The Department for Health said medical professionals would be on hand to provide assistance if needed.
They added: "The enhanced monitoring of direct flights will be kept under continuous review and expanded to other Chinese departure points if necessary."
- ITV News Health Correspondent Emily Morgan explains how the UK is dealing with the risks:
While no one will be allowed to leave Wuhan, the Foreign Office is advising against "all but essential travel" to the city.
“In light of the latest medical information, including reports of some person-to-person transmission, and the Chinese authorities’ own advice, we are now advising against all but essential travel to Wuhan," a spokesperson said.
“The safety and security of British nationals is always our primary concern, and we advise British nationals travelling to China to remain vigilant and check our travel advice on gov.uk.”
Currently, no one in the UK has developed coronavirus, but PHE has increased the risk to the country from "very low" to "low".
Dr Nick Phin, Deputy Director, National Infection Service, PHE, said anyone who has recently visited Wuhan "should seek medical attention if they develop respiratory symptoms within 14 days of visiting Wuhan, either in China or on their return to the UK".
It is thought that coronavirus can spread from human-to-human in the same way as common colds and the flu - through coughs, sneezes and contact with an infected service.
There are also fears that the virus is mutating, making it harder to deal with.
Initial symptoms include headaches, fevers and coughs, but it can progress to pneumonia and cause breathing difficulties.
For people with pre-existing health conditions coronavirus can be, and already has, proved fatal.
- Watch: What is coronavirus and what are the symptoms?
What is the disease and how far has it spread?
The illness comes from a newly identified type of coronavirus, a family of viruses which can cause the common cold, as well as more serious illnesses such as SARS, which spread from China to more than a dozen countries in 2002-2003 and killed about 800 people.
Thailand has confirmed four cases, involving a Thai national and three Chinese visitors.
Japan, South Korea, Macao, the United States and Taiwan have all reported one case each.
All of the illnesses were of people from Wuhan or who recently had traveled there.
What do the experts say?
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.
Gao Fu, the head of the Chinese Center for Disease Control, said officials were working on the assumption the outbreak resulted from human exposure to wild animals which were being traded illegally at a food market in Wuhan.
He added they believed the disease was mutating.
Health officials confirmed earlier this week that the disease can be spread between humans after finding two cases of people in southern Guangdong province who had not been to Wuhan.
It is not clear how contagious it is, but person-to-person transmission could allow it to spread more widely.
The World Health Organization (WHO) is expected to declare an international emergency in response to the outbreak.