The final countdown to the Olympics 2020 bid has begun. Tokyo is now hoping that the recent leaks of highly radioactive water from the Fukushima nuclear power plant won't affect its image as the safest choice among the bids.

On Sunday, the operator of Japan's Fukushima nuclear plant said radiation at a storage tank had spiked 18-fold, a level so high it could kill anyone exposed within hours.

Workers from Tokyo Electric Power Company have also recorded high levels of radioactivity in two other tanks. Last week the company admitted 300 tonnes of highly radioactive water had seeped out of one tank and could have leaked into the sea. Fukushima is 250 kilometres north of Tokyo.

Tokyo Governor, Naoki Inose, has stressed that Tokyo and its surrounding areas have not been affected by the leaks, adding that the city is making transparency on the issue a priority.

"Tokyo is safe, secure and stable. I believe it is here where the future lies," Inose said.

"This is an issue which certainly needs to be resolved, but our understanding is that this is an issue restricted to a certain area. The radiation has not affected Tokyo or its surrounding areas. What's most important is the transparency and immediate release of information."