The move was suggested by a Government panel following a complaint of irregularities in an earlier bid round this summer, and looks set to delay demolition of the Stadium to clear the way for a new structure to host the Olympics until at least the middle of December, five months later than planned.

"There was a complaint about the process and it was recommended to us that we hold another round of bidding," an official at the Japan Sport Council (JSC), which owns and runs the Stadium originally built when Tokyo hosted the 1964 Olympics, told Reuters.

"We accepted that suggestion," he said, adding that the job would be awarded in November and work should begin before the end of the year.

The first round of bids to demolish the Stadium failed because all the bids were too high, the JSC said, and a second round was held at the start of the summer.

The main Olympic site for the Tokyo 2020 Games is due to be on the site of the Olympic Stadium used to host the event in 1964 ©Getty Images

A Tokyo construction company subsequently filed a complaint with the Government Procurement Review Board, a branch of the Cabinet Office, about the results.

The daily Tokyo Shimbun quoted workers at that construction firm and several others in Tokyo as saying the bids were opened before setting the final price and the job was then awarded to a company other than the lowest bidder.

"We had an internal probe of the matter and verified that this did not happen," the JSC official said.

The Government Procurement Review Board said there was no proof of misdoing, but there appeared to be some problems with fairness and called for another round of bidding.

Minister of Education, Culture, Sports, Science and Technology Hakubun Shimomura, whose Ministry is in charge of preparing for Tokyo 2020, told reporters he had heard the bid process involved some "basic mistakes".

"This is extremely regrettable and we are taking it extremely seriously," he said.

"We are recommending that another round of bidding be held."

Plans for the Stadium by Zaha Hadid, who also designed the Aquatics Centre for London 2012, were criticised soon after Tokyo won the Games last year because of rising cost estimates and a lack of harmony with the surrounding cityscape.

The new stadium, set to have 80,000 seats, up from 54,000 now, is due to be completed in time for the Rugby World Cup in 2019, a deadline the JSC official said there would still be no problems in meeting.

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