World governments rushed to contain a new, heavily mutated Covid-19 strain Sunday, with borders closing and Australia reporting its first cases of the variant.

The variant now known as Omicron has stoked fears that it is highly infectious.

Scientists are racing to determine the threat posed by the heavily mutated strain -- particularly whether existing vaccines work.

Several countries have also announced plans to restrict travel from southern Africa, where it was first detected, including Qatar, the United States, Britain, Saudi Arabia, Kuwait and the Netherlands.

Israel said on Sunday it would close its borders to all foreigners in a bid to curb the spread of the variant, and Japan made a similar announcement on Monday.

But the virus strain has already been found everywhere from the Netherlands to Hong Kong and Australia, where authorities Sunday said they had detected it for the first time in two passengers from southern Africa who were tested after flying into Sydney.