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

The pandemic has already forced a year-long delay of the Games -- which are now scheduled to open on July 23, 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 noted 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."

Masa Takaya, a Tokyo 2020 spokesman, declined to comment on a possible cancellation of the Games, telling reporters that Mori's remarks were based on "the chairman's own thoughts".

Japanese organizers and the International Olympic Committee, under heavy pressure from athletes and international sports federations, agreed in March to a year-long postponement of the Games.

Organizers 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 has 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 criticized the country's response to the coronavirus warned that he was "very pessimistic" that the postponed Olympics can be held in 2021.

"To be honest with you I don't think the Olympics is likely to be held next year," said Kentaro Iwata, a professor of infectious diseases at Kobe University, at a briefing.

But Tokyo 2020 spokesman Takaya countered that even medical experts said it was too early to make a judgement on such a possibility.

In the interview, Mori also said organizers were considering holding joint opening and closing ceremonies for the Olympics and the Paralympics in an effort to cut costs.

Under the plan, the Paralympics would join the Olympic opening ceremony on July 23, and the Olympic closing ceremony would be integrated into the Paralympics closing event in September.

But Mori admitted that Tokyo organisers had not yet obtained the consent of the IOC and their Paralympic counterparts on that plan.

"It's going to a considerable cut in costs and a big message of victory against the global crisis, but it's not easy," Mori said.