An athlete with the Serbian Olympic team has tested positive for coronavirus after arriving in Japan, less than three weeks before the Games, a host city official said Sunday.

The member of the five-strong rowing team was found to have contracted the virus after a test at Tokyo's Haneda airport upon arrival Saturday, according to an official of Nanto, a central Japanese city, where the team planned to train ahead of the Olympics.

The athlete has been isolated, while the remaining four have been transferred to a separate facility near the airport, the official said.

"The members were scheduled to arrive in our city today and start training, but the entire programme is likely to be cancelled," the official told AFP.

The case came as organisers prepare to tighten screening procedures at airports after two members of Uganda's team tested positive following their arrival in Japan last month.

Hidemasa Nakamura, a senior Tokyo 2020 Games official, said last week that Olympic teams should be immediately isolated if they arrive in Japan with a person infected with coronavirus.

Public opinion has been firmly opposed to holding the Games this year over pandemic fears, though recent polls suggest opposition may be softening.

No overseas fans will be allowed and domestic spectators will be capped at 10,000 per event.