PARIS - Japan and France confirmed their first cases of the new variant of the coronavirus on Tuesday as countries around the world scrambled to close their doors or find ways to limit its spread while scientists study how damaging it might be.

The World Health Organization has warned that the global risk from the omicron variant is "very high" based on early evidence, saying it could lead to surges with "severe consequences."

French authorities on Tuesday confirmed the first case of the omicron variant in the French island territory of Reunion in the Indian Ocean. Patrick Mavingui, a microbiologist at the island's research clinic for infectious diseases, said the person who has tested positive for the new variant is a 53-year-old man who had traveled to Mozambique and stopped in South Africa before returning to Reunion.

The man was placed in quarantine. He has "muscle pain and fatigue," Mavingui said, according to public television Reunion 1ere.

Japan on Tuesday confirmed its first case in a visitor who recently arrived from Namibia, a day after banning all foreign visitors as an emergency precaution against the variant. A government spokesperson said the patient, a man in his 30s, tested positive upon arrival at Narita airport on Sunday and was isolated and is being treated at a hospital.

Cambodia barred entry to travelers from 10 African countries, citing the threat from the omicron variant. The move came just two weeks after Cambodia reopened its borders to fully vaccinated travelers on Nov. 15.

The new version was first identified days ago by researchers in South Africa.

WHO said there are "considerable uncertainties" about the omicron variant. But it said preliminary evidence raises the possibility that the variant has mutations that could help it both evade an immune-system response and boost its ability to spread from one person to another.

The WHO stressed that while scientists are hunting evidence to better understand this variant, countries should accelerate vaccinations as quickly as possible.

Despite the global worry, doctors in South Africa are reporting patients are suffering mostly mild symptoms so far. But they warn that it is early. Also, most of the new cases are in people in their 20s and 30s, who generally do not get as sick from COVID-19 as older patients.