A flight to bring about 200 British nationals back to the UK from coronavirus-hit Wuhan is unable to take off as planned on Thursday.
It is understood relevant permissions from Chinese officials have not yet come through.
The Foreign Office said it was “working urgently” to organise a flight to the UK “as soon as possible”.
The virus has caused at least 170 deaths, spreading to every Chinese region and at least 16 other countries.
The flight from Wuhan, the city where the virus first emerged, had been expected to arrive at RAF Brize Norton in Oxfordshire on Thursday morning. Passengers were to be taken to an NHS facility.
When the passengers do return they will be put in “supported isolation” for 14 days with “all necessary medical attention”, a Downing Street spokesman said.
The Foreign Office said a number of other countries’ flights had also been unable to take off as planned.
“We remain in close contact with the Chinese authorities and conversations are ongoing at all levels,” a spokeswoman said.
Chinese health authorities said there were 7,711 confirmed coronavirus cases in the country as of Wednesday night.