Travellers from Tanzania and the Democratic Republic of Congo will be banned from coming into the UK in an attempt to block the South African Covid-19 variant.
But the ban - which will come into force from 4am on Friday - will not apply to British and Irish nationals and those with residency rights returning to the country, Transport Secretary Grant Shapps said.
It comes after the UK's chief scientific adviser Sir Patrick Vallance warned vaccines currently being rolled out may be less effective against the South African variant.
The new variant - known as 501Y.V2 and thought to be about 50% more infectious - is believed to be more transmissible than the UK one.
And a study by researchers from South Africa, which has not yet been peer-reviewed, found that the South African variant contains mutations that may be resistant to immunity from previous coronavirus infection.
Mr Shapps tweeted: “To help to stop the spread of the Covid-19 variant identified in South Africa, we are banning all arrivals from Tanzania and Democratic Republic of Congo from 4am tomorrow.
“All passengers from these countries except British and Irish Nationals and third country nationals with residents rights will be denied entry.
“We are continuing to monitor Covid-19 rates and new strains of the virus across the globe, this alongside the suspension of travel corridors and pre-departure testing will help protect our borders.”
Matt Hancock said at the beginning of January that he is "very worried" about the South African variant. Flights from South Africa to the UK have already been banned since December 23.
More countries around the southern part of Africa were added to the list on January 9: Namibia, Zimbabwe, Botswana, Eswatini, Zambia, Malawi, Lesotho, Mozambique and Angola – as well as the Seychelles and Mauritius.