The postponed Tokyo 2020 Olympics will be cancelled if the coronavirus pandemic isn't brought under control by next year, the organising committee's president said in comments published on Tuesday.

The pandemic has already forced a year-long delay of the Games, which are now scheduled to open on 23 July 2021, but Tokyo 2020 president Yoshiro Mori said no further postponement was possible.

In an interview with Japan's Nikkan Sports daily, Mori was categorical when asked if the Olympics could be delayed until 2022 if the pandemic remains a threat next year, replying: "No."

"In that case, it's cancelled," Mori said.

Mori said the Games had been cancelled previously only during wartime and compared the battle against coronavirus to "fighting an invisible enemy".

If the virus is successfully contained, "we'll hold the Olympics in peace next summer", he added. "Mankind is betting on it."

Under heavy pressure from athletes and sports associations, Japanese organisers and the International Olympic Committee (IOC) agreed in March to a year-long postponement of the Games.

Organisers and Japanese officials have said the delayed Olympics will be a chance to showcase the world's triumph over the coronavirus, but questions have arisen about whether even a year's postponement is sufficient.

On Tuesday, the head of Japan Medical Association warned it would be "exceedingly difficult" to hold the Games next year if a vaccine had not been found.

"I would not say that they should not be held, but it would be exceedingly difficult," Yoshitake Yokokura told reporters at a briefing.

And last week a Japanese medical expert who has criticised the country's response to the coronavirus warned that he was "very pessimistic" that the postponed Olympics can be held in 2021.