Tokyo Olympics organizers revealed the first COVID-19 case in the Games Village on Saturday as they sought to reassure competitors that the pandemic-delayed event would be safe.

Six days before the opening ceremony, organizers said an unnamed person had tested positive for coronavirus in the Village, where thousands of athletes and officials will stay during the Games.

"There was one person in the Village. That was the very first case in the Village that was reported during the screening test," Masa Takaya, spokesman for the Tokyo organising committee, told a press conference.

"Right now this person is confined to a hotel," Takaya said.

Japanese media reported that the person who had tested positive was a foreign national. The Games are facing opposition from the Japanese public, who fear a fresh wave of infections.

Seiko Hashimoto, the chief organiser of the Tokyo 2020 Games, said organisers were ready to respond swiftly if there was a wider outbreak.

"We are doing everything to prevent any Covid outbreaks. If we end up with an outbreak we will make sure we have a plan in place to respond," she said.

Hashimoto conceded that competitors at the Games, which were postponed for a year because of the pandemic, would be anxious about the virus situation -- and she vowed that organiers would not hide cases.

"Athletes who are coming to Japan are probably very worried. I understand that," she said.

"That is the reason why we need to make full disclosure." 

Tokyo 2020 CEO Toshiro Muto said it was not yet known if the person had been vaccinated against Covid-19.

"We don't have any information on whether this person was vaccinated or not," Muto said.

He said competitors at the Games would be tested every day "so if someone tests positive, that person will be isolated immediately whether there are any close contacts or not".