Six African countries are being added to the red list as the UK Health Security Agency investigates a new "more transmissable" Covid variant.
Secretary of State for Health and Social Care Sajid Javid revealed the news on Twitter on Thursday.
The six nations will be temporarily banned, and UK travellers who return from those nations will have to quarantine.
Flights from South Africa, Namibia, Lesotho, Botswana, Eswatini and Zimbabwe will be suspended from midday on Friday and all six countries will be added to the red list, Health Secretary Sajid Javid said.
Read more: Everything we know about the highly evolved Covid super variant
The tweet read: "COVID-19 UPDATE:
"@UKHSA is investigating a new variant. More data is needed but we're taking precautions now.
"From noon tomorrow six African countries will be added to the red list, flights will be temporarily banned, and UK travellers must quarantine."
This comes after a new 'super variant' was identified in ten people from three countries.
According to the Press Association, Mr Javid said: "The early indication we have of this variant is it may be more transmissible than the Delta variant and the vaccines that we currently have may be less effective against it.
"Now, to be clear, we have not detected any of this new variant in the UK at this point in time.
"But we've always been clear that we will take action to protect the progress that we have made.
"So, what we will be doing is from midday tomorrow we will be suspending all flights from six southern African countries and we will add in those countries to the travel Red List.
"Those countries are South Africa, Namibia, Lesotho, Eswatini, Zimbabwe and Botswana. We will be requiring anyone that arrives from those countries from 4am on Sunday to quarantine in hotels.
"If anyone arrives before then they should self-isolate at home and take a PCR test on day two and day eight. And if anyone has arrived from any of those countries over the last 10 days, we would ask them to take PCR tests."
The first cases of the new strain were collected on November 11. There have been ten confirmed cases.
The strain, designated a Variant Under Investigation on November 24, has been labelled B.1.1.529.
It's not know whether vaccination will provide full protection against variant B.1.1.529.
The strain has been detected in three countries around the world: Botswana, South Africa, and Hong Kong.
The only case identified in Hong Kong was in someone who had recently travelled from Africa. This has sparked some concern that the variant is already spreading through international travel.
Three cases have been detected in Botswana and six in South Africa.
The Hong Kong case was a 36-year-old man who travelled to South Africa on October 23 and returned on November 11.
He tested negative on his return to Hong Kong but went on to test positive on November 13 while undergoing quarantine at a hotel.
Due to the number of mutations in the virus, there is some concern that this variant may be able to evade antibodies from previous infections and vaccinations.
However, the best way to protect yourself against all coronavirus strains is to get vaccinated, wear a mask when indoors, and respect any safety measure in place in specific venues.
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