Countries around the world are racing to introduce travel bans and restrictions on southern African countries in an effort to contain a new variant of Covid-19, called Omicron.
The moves come after the variant was officially named by health officials.
Early evidence suggests Omicron has an increased re-infection risk, the World Health Organization (WHO) says.
Meanwhile, hundreds of passengers arriving in Amsterdam from South Africa were tested for the new variant.
Some 61 people on two KLM flights tested positive for Covid-19 and have been quarantined at a hotel near the airport while they have further tests, Dutch officials said.
Passengers travelling from Cape Town to Manchester via Amsterdam told the BBC that they were held on the tarmac at Schiphol airport for four hours, before eventually disembarking.
The Netherlands is currently struggling with a record-breaking surge in cases. A partial lockdown – involving early closure of bars, restaurants and most shops – comes into force there on Sunday.
The new Omicron variant was first reported to the World Health Organization from South Africa on 24 November.
It has also been identified in Botswana, Belgium, Hong Kong and Israel.
unless they are UK or Irish nationals, or UK residents.
US officials said flights from South Africa, Botswana, Zimbabwe, Namibia, Lesotho, Eswatini, Mozambique and Malawi would be blocked, mirroring earlier moves taken by the EU. They will come into effect on Monday.
A host of other countries have also announced restrictions, including the following:
The WHO said the number of cases of this variant, initially named B.1.1.529, appeared to be increasing in almost all of South Africa’s provinces.
“This variant has a large number of mutations, some of which are concerning,” the UN public health body said in a statement.
It said “the first known confirmed B.1.1.529 infection was from a specimen collected on 9 November”.
The WHO said it would take a few weeks to understand the impact of the new variant, as scientists worked to determine how transmissible it was.
A top UK health official warned that vaccines would “almost certainly” be less effective against the new variant.
But Professor James Naismith, a structural biologist from the University of Oxford, added: “It is bad news but it’s not doomsday.”
Only about 24% of South Africa’s population is fully vaccinated, which could spur a rapid spread of cases there, Dr Mike Tildesley, a member of the Scientific Pandemic Influenza Modelling group (Spi-M), told the BBC on Friday.
Meanwhile, US infectious disease chief Dr Anthony Fauci said that while the reports on the new variant threw up a “red flag”, it was possible that vaccines might still work to prevent serious illness.