The new mutation, which is potentially more transmissible, was first discovered in South Africa and has since been detected in Australia, United Kingdom, Germany, Israel, Italy, the Czech Republic and Hong Kong.

Israel is banning all foreigners from entering the country in response to Omicron fears, authorities announced Saturday.

The ban, pending government approval, is expected to last two weeks. Israelis returning from a country on the red list, which includes countries in southern Africa, will be required to isolate for seven days in a designated hotel.

There are seven suspected cases of the variant in Israel, in addition to one confirmed case found in a person returning from Malawi, its Health Ministry said.

The two travellers are in isolation along with 12 other passengers who came from southern Africa, the department said.

Both cases are people who are fully vaccinated and asymptomatic, it added.

Australia has banned the entry of foreigners who have travelled to nine southern African countries in the past 14 days, including South Africa, Lesotho, Botswana, and Zimbabwe.

South Korea has imposed restrictions on travellers from eight southern African countries, its Disease Control and Prevention Agency announced Saturday.

Along with the ban, the issuing of visas for nationals from South Africa, Botswana, Namibia, Zimbabwe, Lesotho, Eswatini, Malawi and Mozambique has been suspended until further notice, the agency said.

Korean nationals entering from those countries must quarantine in a government-designated facility for 10 days.

What's happening in Europe?

Europe is also frantically imposing travel bans and scrambling to ramp up its coronavirus sequencing abilities after several countries on the continent reported suspected Omicron cases.

At least 13 people who got tested at Amsterdam Schiphol airport after traveling from South Africa on Friday tested positive for the Omicron coronavirus variant, Dutch health authorities said on Sunday.

The Netherlands' National Institute for Public Health and the Environment said in a statement that the variant had been detected through the sequencing of the 61 positive COVID-19 results obtained by local health authorities at the airport on Friday.

The travellers, from South Africa, who tested positive were sent into isolation at a nearby hotel, the Dutch authorities added.

A suspected case of the variant was discovered in Innsbruck, western Austria, after a traveller who recently arrived from South Africa tested positive for Covid-19, the Tyrol state government said Saturday.

Samples from the case have been sent to the capital of Vienna, and results are expected in the coming days, authorities said.

Meanwhile, scientists at the Regional Hospital in Liberec, Czech Republic, told CNN Saturday that one case of the Omicron variant was detected in a traveller who arrived from Namibia. Eight other people that travelled with the infected person are also being checked for Covid-19 and the variant, according to CNN affiliate CNN Prima.

UK Secretary of State for Health Sajid Javid said the two cases detected in the UK were linked to travel to southern Africa, the region where the Omicron variant was first detected.

"These individuals are self-isolating with their households while further testing and contact tracing is underway," he added.

The German cases, identified in Munich, are two passengers who arrived from Cape Town on November 24, the Bavarian Ministry of Health said in a statement on Saturday.

"The individuals have been in domestic isolation since November 25 following a positive PCR test," authorities said.

"Following reports of the new variant, the two individuals had the foresight to arrange for themselves to be tested for the variant."

Earlier on Saturday, German authorities had identified a "suspected" case of the Omicron variant in Frankfurt from another passenger who returned from South Africa. The local health department said it should be able to confirm the full sequencing of the virus in this patient on Monday.

The Italian case is in the southwestern region of Campania, a passenger who arrived from Mozambique, Italy's Health Ministry said in a statement. It didn't disclose the date of the passenger's arrival or nationality.

The French government extended its suspension of flights from seven southern African countries on Sunday. The ban was scheduled to be in place until midnight on Sunday evening but was extended to midnight Tuesday evening.

The Centres for Disease Control and Prevention said no known Omicron cases have been identified in the United States, and that if the variant emerges, the agency expects cases would be quickly identified through the nation's variant surveillance system.

The top infectious disease expert in the United States, Dr Anthony Fauci, told NBC Saturday he would not be surprised if the variant was already in the US but had gone undetected.

"When you have a virus that is showing this degree of transmissibility and you're having travel-related cases they've noted in other places already, when you have a virus like this, it almost invariably is going to go all over," the CDC director said.

But while the WHO designated Omicron a "variant of concern" on Friday, it stressed more research was needed to determine whether the variant was more contagious, whether it caused more severe disease, and whether it could evade vaccines.

"This variant has a large number of mutations and some of these mutations have some worrying characteristics," Maria Van Kerkhove, WHO's technical lead for COVID-19, said in a statement on Friday.

"Right now there are many studies that are underway ... so far there's little information but those studies are underway so we need researchers to have the time to carry those out and WHO will inform the public and our partners and our member states as soon as we have more information," she said.

Lawrence Young, a virologist and a professor of molecular oncology at Warwick Medical School in the United Kingdom, said the Omicron variant was "very worrying".

"It is the most heavily mutated version of the virus we have seen to date," he said.

"This variant carries some changes we've seen previously in other variants but never all together in one virus. It also has novel mutations."

Scientists have praised South African health authorities for their quick reaction to a COVID-19 outbreak in the country's Gauteng province, which led to the discovery of the new variant.

When cases in the province started to rise at a higher rate than elsewhere, health experts focused on sequencing samples from those who tested positive, which allowed them to quickly identify the B.1.1.529 variant.

Sharon Peacock, a professor of Public Health and Microbiology at the University of Cambridge, said the South African Health Ministry and its scientists "are to be applauded in their response, their science, and in sounding the alarm to the world".

She said the development showed how important it was to have excellent sequencing capabilities and to share expertise with others.

That message was reinforced by the WHO, which on Friday called on countries to enhance their surveillance and sequencing efforts to better understand coronavirus variants.