TOKYO (AFP) - The Tokyo Olympics chief said the Games would be cancelled only in extreme circumstances on Thursday (June 3) as organisers revealed 10,000 volunteers had quit over coronavirus fears, a sexism row and scheduling problems.

Exactly 50 days before the opening ceremony, Tokyo 2020 president Seiko Hashimoto said the show would go on unless the pandemic stops a majority of teams from travelling.

"If various countries around the world experience very serious situations, and delegations from most countries can't come, then we wouldn't be able to hold it," she told the Nikkan Sports daily.

"But conversely, unless such a situation emerges, the Games will not be cancelled."

The 2020 Games, due to open a year late on July 23, remain beset by doubts and low public support as Japan battles a fourth virus wave with much of the country, including Tokyo, under a state of emergency.

Late on Wednesday, Tokyo 2020 chief executive officer Toshiro Muto said around 10,000 of the 80,000 volunteers - vital to the smooth running of the Games - had quit, largely over coronavirus concerns.

Others dropped out after the Games were postponed, or in protest at sexist remarks made by Hashimoto's predecessor who was forced to resign, Muto told Japanese media.

Former Tokyo 2020 chief Yoshiro Mori stepped down in February after causing a furore by saying that women talk too much and waste time in meetings.

However, Muto said the reduction in volunteers would not affect the Games because the event has been scaled back, so fewer people are needed.

Overseas fans have already been barred, and a decision on whether to allow domestic spectators is expected after the state of emergency in Tokyo ends on June 20.

The number of overseas officials and participants has been cut by about half, to around 78,000, with calls for further reductions.

Medal ceremonies

As the coronavirus continues to overshadow the Olympic build-up, organisers will unveil details of the medal ceremonies later on Thursday - the latest attempt to generate positive momentum.

Polls show 80 per cent of Japanese oppose hosting the Games this year. But surveys among the population of Tokyo have found a more even split between those in favour and against.

Hashimoto said she believed the tide of public opinion could be turning as Japan's initially slow vaccine campaign begins to speed up.

"We are hearing more and more voices from people saying, 'If this is the case, the Olympics may be able to take place'," she said, reiterating that the Games will be safe for all.

Australia's softball team this week became the first Olympic athletes to arrive in Japan, a major step forward.

But in a sign of the challenges ahead, a member of Ghana's Under-24 Olympic football team tested positive upon arriving in Japan for a friendly late on Wednesday, the Japan Football Association said.

All of Ghana's team, who will play Japan's U-24s on Saturday, tested negative in the 72 hours before their departure.

Japan has seen a smaller Covid-19 outbreak than many countries, with just over 13,000 deaths. Around 2.9 per cent of the population has been fully vaccinated.