Japan has imposed a ban on foreigners, following Israel's lead.

Japan announced on Monday that it would seal its borders to foreigners, joining Israel in implementing the harshest steps against the Omicron coronavirus type, which the WHO claimed posed a "very high" global risk of outbreaks.

Markets regained their composure as investors awaited further details on the variant, which had plummeted last week on expectations that it would impose new restrictions, jeopardising the economy's fledgling recovery from a two-year slump.

Omicron was first discovered in southern Africa and has since been found in Australia, Belgium, Botswana, the United Kingdom, Canada, Denmark, France, Germany, Hong Kong, Israel, Italy, the Netherlands, and Scotland.

The Omicron form is likely to spread internationally, with "severe consequences" in some locations, according to the World Health Organization (WHO).

"The overall global risk related to the new variant of concern Omicron is assessed as very high," the World Health Organization stated, adding that determining the severity of the variant could take weeks.

Japan would seal its borders to foreigners beginning Tuesday as a precaution to avoid a worst-case situation, Prime Minister Fumio Kishida said, adding that he was prepared to face criticism for being overly cautious.

"These are temporary, exceptional measures that we are taking for safety`s sake, until there is clearer information about the Omicron variant," Kishida told reporters.

He did not specify how long the ban will be in effect. Quarantine would be imposed on Japanese returning from specific countries, he added.

While no Omicron infections have been discovered in Japan, Health Minister Shigeyuki Goto said the country is conducting tests to see if the strain affected a Namibian visitor who tested positive for the virus.

Israel, where the ban went into effect at midnight on Sunday, has pledged to tackle the new variant using counter-terrorism phone-tracking equipment.

After reporting the first Omicron cases, Australia said it will rethink plans to reopen its borders to skilled migrants and students starting Dec. 1. Prime Minister Scott Morrison said a national security panel would convene later in the day, but that it was "a bit too early" to reinstate the two-week hotel quarantine for foreign visitors.

"So we just take this one step at a time, get the best information, make calm, sensible decisions," Morrison said.