A Tokyo panel on Thursday urged changes to three venues for the 2020 Olympics in the face of ballooning costs but organisers say such adjustments might prove difficult to instigate in time for the Games.
Tokyo touted access to a $US4.5 billion ($A5.9 billion) ($A5.9 billion) ($A5.9 billion) war chest when it beat Madrid and Istanbul in its successful 2013 bid for the Summer Games, but recently elected governor Yuriko Koike campaigned on reining in escalating costs and ordered a review of expenses.
The proposed changes, which could include moving rowing and canoeing some 400km from Tokyo, would require the approval of the International Olympic Committee (IOC) and each sport's international federation.
They are the latest in a series of embarrassing setbacks and broken promises for organisers, who had won the bid largely on Japan's reputation for efficiency.
Tokyo's bid proposal said some 85 per cent of venues would be within 8km of the Olympic Village in central Tokyo.
According to a preliminary report, released on the same day as an executive board meeting of the Tokyo 2020 organising committee, overall costs could surge to more than four times original estimates of 734 billion yen ($A9.42 billion).
"Given the current situation, costs could run over 3 trillion yen ($A38 billion)," the panel wrote in its report.
When it won the Games, Tokyo said it would bring in economic benefits of 3 trillion yen and create 150,000 jobs.
To cut back, the panel proposed reconsidering the construction of three new venues -- for volleyball, swimming and rowing/canoeing -- in favour of using existing venues.