Holding the postponed Tokyo Olympics this summer will be "really difficult" given a spike in coronavirus infections across Japan, the head of the Tokyo Medical Association has warned.

Haruo Ozaki sounded the alarm as rising daily cases prompt new virus restrictions in Tokyo and elsewhere in Japan.

"If infections spread further, in reality it would be difficult to hold the Olympics in its regular form with athletes coming from various countries, even if the Games are held with no spectators," the Sports Hochi daily quoted him as saying at a Tuesday press conference.

On his Facebook page Wednesday, Ozaki said the report reflected his concerns, even though recent successes by Japanese swimmer Rikako Ikee and golfer Hideki Matsuyama had been inspiring.

"I couldn't hold back my tears watching Ikee and Matsuyama's great performances. I want to watch their great performances at the Olympics too," he wrote.

"But, from my position as the head of medical workers, I have to say that holding the Games is really difficult."

Ozaki called on organisers to "show concrete measures on how they can prevent the spread of infection at home and abroad."

"Then we would like to sincerely study if such a plan is realistic," he wrote.

The comments come as Tokyo marks 100 days until the virus-postponed 2020 Olympics open on July 23.

Rising daily cases have prompted new virus restrictions in Tokyo and elsewhere in Japan
Rising daily cases have prompted new virus restrictions in Tokyo and elsewhere in Japan AFP / Charly TRIBALLEAU

The rise in Covid-19 cases in Japan and abroad is fuelling concerns about whether the Games can, or should, go ahead.

New virus restrictions have been put in place in several parts of Japan, including Tokyo and Osaka.

The measures are significantly looser than lockdowns seen in other parts of the world, but they have forced the Olympic torch relay off public roads in Osaka.

Instead, the flame is being carried along a closed course inside a park with the public kept away.

Olympic organisers have released a series of virus rulebooks they say will keep the Games safe.

They will bar overseas spectators, limit the movement of athletes and require regular virus testing.

But vaccination will not be required and quarantine rules will be waived for Olympic participants.

Polls show a majority of people in Japan want the Games postponed or cancelled.

Support for holding the event this summer has risen since a winter surge in infections, but still hovers below 30 percent.

Coronavirus