The Foreign Office has issued new travel advice over the Coronavirus outbreak in China.
In updated guidance, it warns against all travel to Hubei province – where the virus began – and urged Britons already there to leave if they can.
The province has been on lockdown for days as the authorities try to contain the virus, which has so far killed at least 50 people.
But some British people in Hubei province say they cannot leave.
The virus originated in the city of Wuhan in that province, and has infected almost 2,000 people since its discovery.
Chinese President Xi Jinping has warned the spread of the virus is accelerating, telling senior officials the country is facing a “grave situation”.
Checkpoints are preventing people from leaving, the airport has been closed, and many of the roads have been closed off to all vehicles except those carrying patients or medical supplies.
The Foreign Office advice says that Wuhan authorities have closed all transport hubs “including airports, railway and bus stations”, while travel restrictions remain in place in other cities in Hubei province.
Some British citizens stranded in Wuhan have criticised the government’s response.
Yvonne Griffiths, a university lecturer from Cardiff, is due to fly home on Monday, but is not confident that will happen: “I am disappointed at the absolute silence on the issue of how stranded people are going to get home.
“And it seems maybe the British government at the moment has either a lack of concern or a lack of planning in place, I’m not sure.”
One British man who had travelled to Wuhan to visit his girlfriend is stranded there after his return flight on 3 February was cancelled.
The 29-year-old, who did not want to be named, told the PA news agency trying to get out of the city is “impossible”.
He said: “There have been sporadic warnings from local government in Chinese to tell us that there will be road closures.
“There is no news on when the airport will reopen therefore the airline [China Southern] have just cancelled the flight.
“I’ve also had no help from the UK Embassy in Beijing who are conveniently closed for the weekend.”
England’s Chief Medical Officer Professor Chris Whitty said there is a “fair chance” cases will emerge in Britain, but tests on 31 people in the UK have come back negative, the government said.
The Department of Health said there are currently “no confirmed cases in the UK or of UK citizens abroad, and the risk to the public is low”.