More countries are tightening their travel restrictions after a new coronavirus variant was identified in southern Africa earlier this week.
The UK and Singapore are among those rushing in stricter quarantine measures or banning flights from South Africa and neighbouring countries.
The EU is proposing to ban flights from the region across the whole bloc.
Scientists still have much to learn about the variant, but say they are very worried about it.
The World Health Organization (WHO) has said it will take a few weeks to understand the impact of the new variant, as scientists work to determine how transmissible it is.
The variant is very different to the others that have emerged so far. Scientists have said it is the most heavily mutated version yet, which means vaccines, which were designed using the original strain from Wuhan, may not be as effective.
The new variant is yet to be given a more memorable name, like Delta or Beta, and right now is known as B.1.1.529. The WHO is expected to name it on Friday, and announce whether it is a variant of concern or just a variant of interest.
The WHO says so far fewer than 100 sample sequences have been reported. Cases have mainly been confirmed in South Africa, but have also been detected in Hong Kong, Israel, Botswana and Belgium.
UK Health Secretary Sajid Javid said on Friday that it is "highly likely" to have spread to other countries.
Most of the cases in South Africa have been from its most populated province, Gauteng, of which Johannesburg is the capital city.
Only about 24% of South Africas population is fully vaccinated, which could see 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.
In Hong Kong, the variant spread during hotel quarantine between a person who had arrived from South Africa and another hotel guest who tested positive a few days later, the Department of Health revealed. Both were fully vaccinated.
Israels Prime Minister Naftali Bennett said on Friday it is "on the verge of a state of emergency" regarding the new variant, and that he would "act fast, strong and now".
One case was detected in a person who returned from Malawi, according to Israeli media reports quoting the countrys health ministry. Another two suspected infections were yet to be confirmed with test results. All three are said to have been fully vaccinated.
The WHO has warned against countries hastily imposing travel restrictions, saying they should look to a "risk-based and scientific approach."
Nevertheless, an increasing number of nations including the UK and the Netherlands have temporarily halted flights from these southern African nations:
Singapore, Italy, France and Israel are among those who have also placed Mozambique, on their red lists.
Japan has announced that from Saturday, travellers from southern Africa will need to quarantine for 10 days and take a total of four tests during that time.
"The key to crisis management is to prepare for the worst," the Japan Times newspaper quoted chief cabinet secretary Hirokazu Matsuno as saying.
The Head of the European Commission, Ursula von der Leyen, has called for all EU nations to put on the "emergency brake" and stop flights from the region.
"It is now important that all of us in Europe act very swiftly, decisively and united," she said on Friday.
The EU is already struggling to cope with fresh waves of the virus, and several countries have re-imposed lockdowns and restrictions.
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The Czech Republic will ban anyone has has spent more than 12 hours in those nations from entering as of Saturday.
Germany, which is currently going through a fourth wave of infections because of the Delta variant, will allow only Germans to fly into Germany from South Africa as of Friday night, a health ministry source quoted by Reuters news agency said. Even if travellers are fully vaccinated, they will still have to spend 14 days in quarantine.
India has ordered more rigorous screening and testing for travellers arriving from South Africa, Botswana and Hong Kong, local media is reporting.
The flight bans threaten to separate families over the festive season.
Ruth Daines-Slack, 70, had booked to fly from Cape Town to the UK next week for Christmas and her mothers 100th birthday celebration. She told the BBC she is "beyond devastated" that she will no longer be able to make the trip, adding that the UKs travel ban is a "knee-jerk reaction".
The UK was one of the first nations to impose a flight ban, which South Africas foreign ministry has criticised as a "rushed decision" made before the WHO has made any announcement on the variant.