UK Health Secretary Sajid Javid said from 12:00 GMT on Friday six countries would be added to the red list, with flights being temporarily banned.

Only 59 confirmed cases have been identified in South Africa, Hong Kong and Botswana so far.

All flights from South Africa, Namibia, Zimbabwe, Botswana, Lesotho and Eswatini are being suspended.

Mr Javid said that scientists were "deeply concerned" about the new variant but more needed to be learned about it.

But he said the variant has a significant number of mutations, "perhaps double the number of mutations that we have seen in the Delta variant".

BBC Africa correspondent Andrew Harding said scientists in South Africa were trying to understand the mutations of the new variant.

He said there was unhappiness at the new red listing by other countries, with scientists saying the country needed more support and more reward for spotting the new variant.

The new variant, which has been designated a new variant under investigation by the UKHSA, is heavily mutated and the confirmed cases are mostly concentrated in one province in South Africa.

Experts in South Africa have said the variant is "very different" to others that have circulated, with concerns that it could be more transmissible but also able to get around parts of the immune system.

It had not been proven that the variant was more transmissible, but it has mutations consistent with the Delta variant and appeared to spread more quickly than other variants, he said.

Imperial College London's Prof Neil Ferguson said it was concerning the new variant appeared to be "driving a rapid increase in case numbers in South Africa" and said the move to restrict travel was "prudent".

But he said it was not clear if the variant was more transmissible or resistant to vaccines and therefore it was too early to judge the risk it poses.

British Airways said it was contacting affected customers and Virgin Atlantic said it would be reviewing its schedule for South Africa for the coming week, with flights from Johannesburg to Heathrow cancelled between 12:00 on Friday and 04:00 on Sunday.

New heavily mutated Covid variant raises concern.