"A deputy governor will serve official duties on her behalf this week as Governor Koike needs a rest due to excess fatigue," a Metropolitan Government spokeswoman told Reuters.

Kyodo News cited sources as saying that Koike had checked in to a hospital in the city.

The announcement comes as preparations for the uniquely complex, postponed Tokyo 2020 Olympics ramp up amid continuing public concerns about coronavirus infections.

Polls have shown most Japanese people remain wary about the possibility that the Games will spread infections, with 435 cases reported on Tuesday.

Koike became the Japanese capital’s first female Governor in 2016, and was re-elected in a landslide vote on July 5 2020, winning 59.7 per cent of the vote.