Japan's 2020 Olympics committee may seek further vaccine donations to make the rescheduled Games as safe as possible, Tokyo 2020's CEO Toshiro Muto says.

But Muto flatly denied there had been any talk of a cancellation or further postponement at Tuesday's executive board meeting.

"There was no talk on that whatsoever," he told reporters.

The Olympics have already been postponed by a year amid global concerns over how organisers can keep volunteers, athletes, officials and the Japanese public safe when they begin on July 23 after a fourth wave of infections.

Muto spoke of possibly seeking further vaccine shots, adding that "there is an ongoing discussion on whether we should be vaccinating Olympic-related staff more widely".

Most people in Japan oppose holding the Games at all, several polls have shown, and a top Japanese virologist and government adviser was quoted on Tuesday as saying it was impossible to have a risk-free Games.

Tohoku University professor Hitoshi Oshitani was an architect of Japan's "Three Cs" approach to the pandemic, which advises avoiding closed spaces, crowds and close contact.

"It's 100 per cent impossible to have an Olympics with zero risk...of the spread of infection in Japan and also in other countries after the Olympics," The Times quoted Oshitani as saying.

"There are a number of countries that do not have many cases, and a number that don't have any variants. We should not make the Olympics (an occasion) to spread the virus to these countries," he added, noting most countries lack vaccines.

However, a former Olympian turned public health expert said she believed the Games can be pulled off with an acceptable level of risk.

"There will be cases, but having one case or a couple of cases doesn't mean that it was a failure," Tara Kirk Sell, a professor at the Johns Hopkins Bloomberg School of Public Health, said.

Playbooks from event organisers detailing testing regimes and movement restrictions for athletes and other visitors "outline a good strategy" for minimising contagion, Sell added.

Media arriving from abroad to cover the Games will be closely monitored to ensure they don't leave pre-registered areas such as hotels and sports venues, Tokyo 2020 President Seiko Hashimoto said.

She also said Japan's Olympics-related staff were expected to start getting vaccinated in mid-June.

"We are still in a very difficult situation, but we have seen a gradual decrease of infections in Tokyo, and I am praying that the pandemic is brought under control as swiftly as possible," Hashimoto said at the start of the Tokyo 2020 board meeting.