Tokyo observed the original date a year ago. That was before the COVID-19 pandemic postponed the Olympics and pushed back the opening to July 23, 2021. Fireworks cascaded over Tokyo Bay back then, and local celebrities unveiled the medals in a highly choreographed show.

There's none of that this time.

Organisers produced a 15-minute, no-fans event on Thursday inside the new national stadium; screening a video to promote next year's opening. They also teased the presence of the Olympic flame, which arrived in Japan in March and had been hidden away ever since.

The low-key event on a rainy day captures the local mood.

A poll a few days ago from Japanese news agency Kyodo repeated the results of recent surveys: Japanese are sceptical the games should go ahead, and doubtful they will.

Organisers and the International Olympic Committee have ruled out another postponement. The Tokyo Games would be cancelled this time if they can't be held.

In an interview on Wednesday with Japanese broadcaster NHK, Yoshiro Mori, the president of the organising committee, was blunt. He was asked: "If this kind of situation (with COVID-19) continues, is it possible to hold the games?"

"If current situation continues, we couldn't," he replied, though he said he was optimistic about a vaccine and confident the pandemic would recede.

Tokyo is staking its hopes on "simplification". Organisers have come up with roughly "200 items" that may be simplified, downsized, or cut out. The rigour is driven by soaring costs and the risk of the Olympics becoming a petri dish.

Estimates in Japan suggest the postponement will cost $US2 billion ($A2.8 billion) to $US6 billion. The IOC and organisers acknowledge the "massive costs" but say it's too early to give a number.

This is on top of the $US12.6 billion that Japan says it's officially spending on the Olympics. However, a national auditor says the real cost is twice that much.

CEO Toshiro Muto has said the 206 national Olympic committees, dozens of sports federations, sponsors, broadcasters, media, and hospitality providers, have been asked to find ways to reduce the size of their delegations arriving in Tokyo.

Muto said organisers are "re-examining service levels and requirements in every possible area". IOC President Thomas Bach has said "nothing is taboo" as billions in costs pile up.

There is one untouchable: the quota of 11,000 athletes and 4400 Paralympians will not be cut, and competition schedules and the 42 venues will remain the same. That opens the way for TV broadcasts to go ahead, the lifeblood of the IOC. The IOC had income of $US5.7 billion over the last four-year Olympic cycle, and 73 per cent was from selling broadcast rights. Another 18 per cent was from top sponsors.

For Tokyo, there are more questions than answers.

Will there be fans? If so, will they be fans from aboard, or only Japanese? Will athletes face quarantines, and will there be a vaccine? Should young athletes be a priority for a scarce vaccine, and will all agree to be vaccinated? How will athletes be safe in the crowded Athletes Village? How about staffing levels for officials, coaches, and tens of thousands who work behind the scenes? Tokyo had planned to use at least 80,000 unpaid volunteers.

"We need to prepare for all the scenarios that may be necessary," said IOC vice president John Coates, who oversees preparations for Tokyo. "We don't know what's going to be necessary. We don't know what the state of COVID-19 is going to be next year. But we need to be preparing for it now."

Australian Associated Press