South Africa said on Friday a British ban on flights from six southern African countries over a new Covid-19 variant seemed rushed, as EU authorities prepared similar moves and the World Health Organization (WHO) convened an emergency meeting.

Scientists have so far only detected the B.1.1.529 variant in relatively small numbers, mainly in South Africa but also in Botswana and Hong Kong, but say they are concerned by its high number of mutations which could possibly make it vaccine-resistant and more transmissible.

Britain said the variant was the most significant one found yet after banning flights from South Africa, Botswana, Lesotho, Eswatini, Zimbabwe and Namibia from midday on Friday.

European Commission chief Ursula von der Leyen said the EU also aimed to halt air travel from the region, describing the variant in a tweet as "of concern".

A WHO working group on virus evolution is due to meet on Friday to discuss whether to officially give it that label, a designation only given to four variants so far.

WHO epidemiologist Maria Van Kerkhove said in a video posted on Twitter that it could take a few weeks to understand the impact of the variant's mutations.

The rand slumped over 2% against the dollar early on Friday, as the variant unnerved investors. South African hospitality stocks also plummeted.

South Africa will speak to British authorities to try to get them to reconsider their ban, the foreign ministry in Pretoria said.

"Our immediate concern is the damage that this decision will cause to both the tourism industries and businesses of both countries," Foreign Minister Naledi Pandor said in a statement.

As Asian countries also moved to tighten curbs, two Welsh rugby clubs in South Africa for a tournament scrambled to leave as soon as possible, and British and Irish golfers withdrew from the Johannesburg Open.

South Africa - the worst affected in Africa in terms of total reported Covid cases and deaths - had been experiencing a lull after a severe third wave of infections, until last week when new infections started to pick up.

On Thursday, the National Institute for Communicable Diseases (NICD) reported 2 465 new cases, almost double the previous day's number. Although the NICD did not link the resurgence to the B.1.1.529 variant, leading local scientists suspect it is the cause.

The Africa Centres for Disease Control and Prevention strongly discouraged travel bans on countries that had reported the variant. "Imposing bans on travellers from countries where a new variant is reported has not yielded a meaningful outcome," it said.