Tokyo Olympics organisers on Sunday (July 18) reported the first COVID-19 cases among competitors residing in the athletes' village.
It comes as its population swells ahead of the start of the pandemic-hit Games next week.
Two athletes from the same country and competing in the same sport staying in the village in the Harumi waterfront district tested positive for the virus, organisers said.
Organisers on Sunday reported 10 new cases connected to the Olympics, down from 15 new cases a day earlier.
South Africa reported three positive cases in its soccer squad.
This the response from the IOC's Olympic Games executive director, Christophe Dubi.
"There is no such thing as zero risk and that we all agree. At the same time, the mingling and crossing of population is incredibly limited."
The new infections are testing the layered testing regime designed to ensure COVID cases are quickly caught and isolated.
Proponents argue that the growing number of cases underscores the strength of the testing system.
Infection rates are climbing among Tokyo's general population, topping 1,000 new cases for five consecutive days.
Polls show many Japanese oppose holding the Games with the influx of overseas visitors it entails.