India and Hong Kong have joined more than a dozen European nations in banning flights and travellers from Britain.
It comes as Prime Minister Boris Johnson convenes a crisis meeting to "discuss the situation regarding international travel, in particular the steady flow of freight into and out of the UK", a spokesman said.
Health authorities in Britain's former colonial territory Hong Kong said UK flights would be banned from Tuesday.
"From midnight there will be no more passenger flights arriving in Hong Kong from the United Kingdom," Hong Kong health secretary Sophia Chan told reporters.
Anyone arriving in Hong Kong who has been the UK in the last 14 days will also have to undergo a longer quarantine, officials said.
Hong Kong's decision will particularly hit students from the city who were studying there and hoping to return home over the Christmas period.
India said it is also temporarily suspending all flights from Britain.
"Considering the prevailing situation in UK. Govt. of India has decided that all flights originating from UK to India to be suspended till 31st December 2020," the aviation ministry said in a tweet.
France has halted all travel from Britain for 48 hours, including anyone transporting goods "by road, air, sea or rail". Source: AP
It said the suspension would come into effect from 11:59 pm (0629 GMT) on Tuesday.
It added that in a "measure of abundant precaution", passengers arriving from Britain on transit flights would be subject to a mandatory RT-PCR test on arrival.
Britain is home to a huge Indian diaspora and there are several flights per day taking hundreds of people between London and New Delhi and London and Mumbai.
A WHO spokeswoman told AFP that "across Europe, where transmission is intense and widespread, countries need to redouble their control and prevention approaches."
A German government source said restrictions on air travel from Britain could be adopted by the entire 27-member EU and that countries were also discussing a joint response over sea, road and rail links.
French President Emmanuel Macron, German Chancellor Angela Merkel, and EU chiefs Ursula von der Leyen and Charles Michel held a conference call on Sunday about the matter, Macron's office said.
Later Sunday, bans on flights from Britain were imposed in the Americas, including by Canada, Chile and Argentina.
US officials, however, signalled they were holding off on the move for now, while Australian Prime Minister Scott Morrison said he was confident existing 14-day quarantine rules for arrivals were sufficient to handle the threat.
Despite growing concerns about the new strain, EU experts believe it will not impact the effectiveness of existing vaccines, Germany's health minister Jens Spahn said.
The assessment was shared by Britain's chief medical officer Chris Whitty.
