The country has detected the first case of the Omicron variant of Covid-19, the Japanese government said on Tuesday.
The infected person is a man in his 30s arriving from Namibia, who tested positive for Covid at Narita airport near Tokyo upon his arrival on Sunday.
On Monday, Japanese Prime Minister Fumio Kishida said the government will in principle ban the entry of all foreign nationals as he pledged to act quickly on concerns over the new Omicron variant, Xinhua news agency reported.
The measure has been implemented starting on Tuesday and will last for about one month. It requires citizens and foreigners with resident status returning from high-risk areas to quarantine for up to 10 days in a government-designated facility.
The Omicron variant was first reported to the World Health Organisation (WHO) by South Africa last week. So far, several European countries, as well as countries and regions including Australia, Canada, Israel and China's Hong Kong, have confirmed infections of the variant.
The WHO has named the strain that contains a large number of mutations a "variant of concern," warning that it may be highly transmissible and pose an increased risk of reinfection to people who have previously been infected with Covid.