The measure goes against WHO recommendations.
Faced with the Omicron variant, Japan on Wednesday asked airlines to suspend new bookings to its territory for a month.
The announcement came as a second case of the Omicron variant was confirmed in the archipelago on Wednesday, in a traveler who arrived from Peru last week.
Japan had already announced on Monday the closure of its borders to all foreign visitors, just three weeks after relaxing certain restrictions to allow the entry of business travelers, students and foreign interns.
The new measures therefore only concern Japanese citizens and foreign residents in Japan, the only ones authorized to enter Japanese soil.
Since South Africa reported the appearance of this new variant last week, many states have closed their borders to that country and its neighbors, sparking anger in the region.
"General travel bans will not prevent the spread" of this variant, said the World Health Organization (WHO) in a technical document.
Faced with the panic which seems to take hold of the planet, the head of the organization, Tedros Adhanom Ghebreyesus, called for “calm” on Tuesday and asked for a “rational” and “proportional” response.
Doubts over Omicron's spread date
He expressed "concern that several member states are taking general and brutal measures which are neither evidence-based nor effective in themselves and which will only worsen inequalities" between countries.
These measures "may have a negative impact on global health efforts during a pandemic by discouraging countries from reporting and sharing epidemiological and sequencing data," the WHO has even warned.
To read also Omicron: where was really born this variant which anguishes the planet?
Officially reported in South Africa on November 24, this visibly highly contagious new variant would in fact have started to spread around the world several days earlier, with Dutch health authorities announcing on Tuesday that Omicron was already circulating in the Netherlands on the 19th. November.
On Wednesday, Nigeria, the most populous country in Africa, announced that it had recorded its first three cases in people who had traveled to South Africa.
A few hours earlier, Brazil reported the first two cases - the first in Latin America - in travelers also coming from South Africa.