Olympics and Japanese officials have forged ahead with the sports spectacle despite opposition in the country to hosting huge numbers of athletes, staff and media - more than 11,000 in the athletes' village alone - dozens of whom have already tested positive.

WHO head Tedros Adhanom Ghebreyesus said the Games should go ahead to demonstrate to the world what can be achieved with the right plan and measures.

"May the rays of hope from this land illuminate a new dawn for a healthy, safer and fairer world," he said, holding aloft an Olympic Games torch as he addressed International Olympic Committee members in the Japanese capital. "It is my sincere hope the Tokyo Games succeed."

Spectators have been barred and restrictions have been imposed in and around Tokyo, where COVID-19 infections have jumped and are projected to spike further, in an effort to minimise health risks among residents and visitors.

Japanese people, only a third of whom have had at least one dose of the vaccine, have been concerned the Olympics could become a super-spreader event.

In a recent poll in the Asahi newspaper, 68 per cent of respondents expressed doubt about the ability of Olympic organisers to control coronavirus infections, with 55 per cent saying they opposed the Games going ahead.

The Games' official opening ceremony on Friday is expected to be a scaled-down, sobering performance, according to Marco Balich, a senior adviser to the Tokyo ceremonies executive producer.

As with the opening ceremony, the women's softball match between gold-medal contenders Japan and Australia was held without spectators, amid buzzing cicadas and polite applause from a few hundred staff at a stadium in Fukushima, which was devastated by the 2011 tsunami and nuclear disaster.

Players standing along the benches under the scorching sun - 30 degrees Celsius by midgame - shouted at the hitters all morning, giving the game a Little League feel.

The game ended after five innings due to a mercy rule as a trio of Japanese two-run homers cleared the fence.

Coronavirus infections continued to take a toll among attendees, however, with at least seven more positive cases bringing the total to more than 75.

Dutch skateboarder Candy Jacobs confirmed she had tested positive for COVID-19 and is pulling out of the Games, along with Chilean taekwondo competitor Fernanda Aguirre.

"I will need some time to let my broken heart heal and recover from this," Jacobs wrote on her Instagram account.

As cases climb in Tokyo, Japanese media reported government adviser Shigeru Omi said Tokyo's daily COVID-19 infections may spike to a record 3,000 in the first week of August.

The capital reported 1,832 new cases on Wednesday, the highest for that day of the week and up by 683 from a week earlier.

Rising infections risk adding to pressure on the already-stretched Japanese medical system.

In the skies above Tokyo, Japanese pilots drew the five Olympic rings in a practice flight for Friday's opening ceremony, recreating a similar stunt at the 1964 Tokyo Games, which were held to highlight the country's recovery from WWII.

Australian Associated Press