The WHO on Friday backed the International Olympic Committee, Japan and host city Tokyo to make the right choices in managing the Covid-19 risks surrounding the pandemic-postponed 2020 Games.

The World Health Organization said certain safety decisions regarding athletes, spectators and the Olympic village and venues could only be taken closer to the Games, which are due to open on July 23.

"It's not whether we will have an Olympics or not -- it's how those individual risks within that framework are being managed," WHO emergencies director Michael Ryan told a press conference in Geneva.

The UN health agency said it was down to the Japanese authorities to decide what level of public attendance could take place at Olympic events.

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Olympics organisers are yet to decide how many fans -- if any -- will be allowed at the Games, with overseas spectators already barred from attending.

A virus state of emergency in Tokyo and other parts of Japan was extended on Friday, with restrictions also imposed in more regions as cases surge.

"We have confidence that the International Olympic Committee, and the whole city of Tokyo, and the government of Japan will make the right decisions regarding how best to manage the risks," Ryan said.

"We will leave it to the authorities in Japan, who are highly competent, to decide what level of attendance could occur in the Olympics."

He said the authorities would have to create an environment of safety around the venues.

"Some of those decisions cannot be made until closer to the event, because it will depend on the epidemiologic situation at that time. So there's not a failing at all on behalf of the organisers that they haven't made certain decisions," said Ryan.

"It is our hope that the Olympics can occur. We've seen sporting events and leagues run very, very safely over the last six months without spectators, with special bubbles and arrangements for athletes."

He said the Games would have to manage the risks around competitor safety, the Olympic village, the stadiums, whether spectators attend, and social mixing around Tokyo during the event.

"We will leave any decisions regarding the extent to which the Olympics have attendance at venues and other decisions to them, as we believe they're applying a very, very systematic risk management approach to protect public health," he concluded.

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