A female US gymnast has tested positive for coronavirus at an Olympic training camp and another athlete is self-isolating, team chiefs and Japanese officials said on Monday.

The gymnast was named by her father as 18-year-old Kara Eaker who is in Japan as a reserve on the squad led by superstar Simone Biles.

Eaker is in isolation, along with another “close contact” on the team, her father Mark told CNN.

He said his daughter tested positive at the team’s training camp in Inzai, a city 30 kilometres east of Tokyo, and added she was not experiencing any symptoms and is fully vaccinated for Covid-19.

The test comes after Tokyo’s Olympic Village – where thousands of competitors are living in a biosecure “bubble” – was hit by a fourth coronavirus case.

“We confirmed today that a teen athlete of the team has tested positive,” said Kimiya Kosaku, an Inzai city official without naming Eaker, adding she arrived in Japan on July 15.

“Another athlete has been categorised as having close contact. She is also staying alone inside her room at their accommodation,” Kosaku said.

Kyodo News said the rest of the team had moved to the Olympic Village on Monday afternoon.

“The health and safety of our athletes, coaches and staff is our top priority,” USOC said in a statement confirming a positive test while also refusing to give a name “out of respect for the individual’s privacy”.

“In alignment with local rules and protocols, the athlete has been transferred to a hotel to quarantine.”

Biles and fellow US gymnast MyKayla Skinner posted images of themselves at the Olympic Village on Instagram, with no reference to the Covid case.

The United States topped the gymnastics medal table at the 2016 Rio Games, with Biles winning four gold medals.

The delayed 2020 Games will finally get under way on Friday in a near-empty Olympic Stadium, with Tokyo under a coronavirus state of emergency after a spike in cases.