A member of Serbia's Olympic rowing team tested positive for the new coronavirus on arrival in Japan, an official said on Sunday, the third Covid-19 infection confirmed among Olympic team members visiting for the Tokyo Games starting this month.

A member of Uganda's Olympic squad tested positive for the virus on arrival in June and a second member was confirmed as having the virus a few days later.

One of Serbia's five-member rowing team tested positive during a screening at Haneda airport on Saturday night, said Takashi Ikeda, an official at the sports section of the central Japan city of Nanto, which had been scheduled to host the Serbians' training camp.

The man in his 30s was sent to a medical facility, while the other four were isolated in a separate facility in Tokyo, Ikeda told Reuters by phone.

"Since they are expected to be isolated for two weeks, the Serbian rowing team is unlikely to come to Nanto for training before the Games," he said.

The group was to have travelled to Nanto in Toyama prefecture on Sunday to hold their training camp through July 18, ahead of the June 23 start of the Games.

Rowing teams from Greece, South Africa and Russia arrived in Nanto earlier this month for training camp, he said.

The Tokyo Games, delayed by a year because of the pandemic, are proceeding amid concern that the influx of thousands of people from around the world could unleash another wave of Covid-19 infections in the country.

Foreign spectators are banned, and the government is considering what limits to place on domestic spectators.

Tokyo reported 716 new Covid-19 infections on Saturday, its highest in more than five weeks, as the nation considers extending pandemic restrictions in the capital just weeks.

Cases totalled 518 on Sunday, up 132 from last Sunday, marking the 15th consecutive days of increases from week-earlier levels, said public broadcaster NHK.