* South Africa detects new COVID-19 variant
* Scientists worried by its many mutations
* Britain, others ban flights from some African countries
* WHO labels variant "of concern", assigns letter Omicron (Adds WHO designation, Downing Street spokesperson)
By Alexander Winning and Tim Cocks
JOHANNESBURG, Nov 26 (Reuters) - South Africa said on Friday that imposing restrictions on travellers from the country because of a newly identified COVID-19 variant was unjustified, after a British ban on flights from southern African countries that others have followed.
Health Minister Joe Phaahla told a media briefing that South Africa was acting with transparency and travel bans were against the norms and standards of the World Health Organization (WHO), which held an emergency meeting over the variant named omicron.
Scientists have so far only detected the variant in relatively small numbers, mainly in South Africa but also in Botswana, Hong Kong and Israel. But they are concerned by its high number of mutations which raised concerns that it could be more vaccine-resistant and transmissible.
The WHO designated omicron as "of concern," its most serious level, following a meeting of its technical advisory group.
British Prime Minister Boris Johnson and South African President Cyril Ramaphosa spoke on Friday afternoon and discussed ways to reopen international travel, a Downing Street spokesperson said.
"Our immediate concern is the damage that this decision will cause to both the tourism industries and businesses of both countries," South African Foreign Minister Naledi Pandor said in a statement.
Ramaphosa will convene an advisory council on Sunday to consider evidence on the variant.
The rand currency slumped as much as 2% against the dollar, and South African hospitality stocks plummeted as investors were unnerved.
Britain said the variant was the most significant found yet and banned flights from South Africa, Botswana, Lesotho, Eswatini, Zimbabwe and Namibia. European Union states also agreed to suspend travel to southern Africa, the presidency of the EU said.
However, Salim Abdool Karim, one of South Africa's top epidemiologists, said a global response was important, noting the delta variant spread to 53 countries within three weeks of being identified.
"So it doesn't really help to close borders... We've got to find solutions to this variant together. And part of that is not to overreact," he told Reuters in an interview, characterising the British travel ban as a "panic reaction" that was understandable.
Scientists expressed frustration at the travel bans, saying the focus should be on getting more people vaccinated in places that have struggled to access sufficient shots. It could take weeks for scientists to fully understand the impact of the variant's mutations.
"This virus can evolve in the absence of adequate levels of vaccination. It's upsetting that it takes this to happen to get the point across," Richard Lessells, a South Africa-based infectious disease expert, told Reuters.
In South Africa about 35% of adults are fully vaccinated, higher than in most other African nations, but half the government's year-end target. While the continent struggled initially to obtain sufficient doses, some countries including South Africa now have too much stock, with vaccine hesitancy and apathy slowing the inoculation campaign.
South Africa has been the country worst affected in Africa in terms of total reported COVID-19 cases and deaths, with nearly 3 million infections and more than 89,000 deaths since the start of the pandemic. It had been experiencing a lull after a severe third wave of infections, until last week when new infections started to pick up.
On Thursday, it reported 2,465 new cases, almost double the previous day's number. On Friday, there was a more modest rise in daily infections to 2,828 new cases.
(Additional reporting by Wendell Roelf in Cape Town, Olivia Kumwenda-Mtambo and Emma Rumney in Johannesburg, and Alistair Smout in London Editing by John Stonestreet, Frances Kerry, Toby Chopra and Cynthia Osterman)