A second virus case linked to the Ugandan Olympic team has been detected after a coach tested positive on arrival in Japan, a city official said Wednesday.

The announcement comes as Olympic officials marked one month until the pandemic-postponed games open in Tokyo on July 23.

NHK said the second positive case was an athlete, but local officials declined to confirm.

Uganda's delegation arrived in Japan on Saturday and headed for a training camp in Izumisano, Osaka Prefecture, but a coach who tested positive on arrival was put in isolation.

Eight delegation members and a coordinator for Izumisano who had accompanied them from Uganda were allowed to continue on to their training base but were asked to stay in their hotel on arrival.

On Tuesday, the city said the team and the coordinator were considered close contacts of the coach and would stay in quarantine until July 3 despite testing negative so far.

But an Izumisano city official said Wednesday that one person in quarantine had now tested positive, declining to specify whether the individual was a team member or the coordinator.

"The results of PCR tests that were done using samples taken on June 22 showed one person tested positive," he said.

"Those nine people who have been identified as having had close contacts (with the coach) ... have been isolated in individual rooms in order to avoid contact with others," he added.