Seven members of Japan's team at the World Athletics Championships, including two marathon runners, have tested positive for Covid-19, organisers said Saturday.
A joint statement from World Athletics, the Japan Association of Athletics Federations and local organisers said the outbreak had hit endurance athletes and staff at the championships in Oregon.
Two marathon runners, four support staff and the head coach of the team had returned positive tests.
The identities of the individuals involved were not disclosed.
The statement said the seven individuals had already been isolated and will remain in isolation for five days.
"Steps are being taken to prevent the spread of COVID-19 both within the Japanese delegation as well as amongst all the teams present for the Championships," the statement said.
"All athletes have been fully vaccinated as a requirement for participation in these Championships."
As a precaution, all remaining members of the Japanese delegation would be required not to share common spaces with other delegations.
It said Japanese team members would "as much as possible, be housed independently to prevent the spread of contamination within the Japanese delegation."
The outbreak comes amid a surge of infections across the United States as new variants of Covid-19 take hold.
The US Centers for Disease Control and Prevention said this week that 21 of Oregon's 36 counties were now deemed to be at "high" risk of the virus.
Earlier Saturday, British athlete Morgan Lake announced she had been forced to withdraw from the World Championships after testing positive for Covid-19.
Lake said she had spent five days in isolation without showing any symptoms but was still testing positive for the virus.
"There's bad timing and there's being exposed to Covid on the week of world champs," Lake wrote on Twitter.
"Absolutely heartbroken to have to watch from my hotel room and whilst I'm grateful to be feeling 100% fine, it's even more frustrating to know that I am physically ready to compete but can't," she tweeted.