British authorities have suspended all flights from South Africa and five other countries in the region in response to the discovery of a highly transmissible new coronavirus variant.
From midday GMT on Friday, direct flights from South Africa, Namibia, Botswana, Zimbabwe, Lesotho and Eswatini will be suspended until further notice.
Announcing the restrictions, the British health secretary, Sajid Javid, said it was possible that current vaccines might be less effective against the heavily mutated variant.
No cases have been discovered in the UK.
South African experts say the B.1.1.529 variant had spread rapidly among students in Pretoria.
Experts from the World Health Organization are due to meet South African officials on Friday.