BUENOS AIRES, Argentina -- Three days ahead of the vote to choose the host of the 2020 Olympics, Tokyo bid officials on Wednesday tried to fend off concerns about a leak of radioactive water at the crippled Fukushima nuclear plant in northern Japan.

Bid leader Tsunekazu Takeda said the water and food in Tokyo are as safe as they are in New York, Paris, London or Buenos Aires.

Tokyo is expected to be a slight favourite ahead of Madrid and Istanbul when the IOC members vote Saturday to choose the 2020 host.

All three cities have problems. Istanbul is trying to explain away massive anti-government demonstrations in June, a string of doping cases and a civil war and chemical attack in bordering Syria. Madrid is saddled with Spain's 27 per cent unemployment and budget worries.

"The radiation level in Tokyo is the same as London, New York and Paris," said Takeda, an IOC member and president of the Japanese Olympic committee. "It's absolutely safe, 35 million people living there in very normal conditions. We have no worries."

Five of the seven questions for Takeda in a news conference dealt with the Fukushima leak.

"The water or food is absolutely safe, the same as here," he repeated. "We are not concerned about this problem in Tokyo."

Takeda answered all but one question in English, switching to Japanese near the end to add emphasis.

"Not one person has been affected by the radiation issue," he said through a translator. "Fukushima and Tokyo are 250 kilometres apart. Since we are quite remote you don't need to be concerned about this issue."

Tokyo calls its bid "a pair of safe hands," emphasizing Japanese technology and its ability to deliver on time. This could attract IOC members who are worried about delays in building venues for the 2016 Rio de Janeiro Olympics. Controversy has also surrounded the 2014 Winter Olympics in Sochi, Russia.

Tokyo scored the highest in the IOC's technical report, but IOC members often vote along regional, political or friendship lines that have little to do with logistic or engineering appraisals.

Tokyo's presentation Wednesday included a demonstration of the country's technology in robotics, featuring a robot named Mirata who simulated fencing with two-time Olympic silver-medallist Yuki Ota.

Although bid officials downplayed concerns, the Japanese government announced Tuesday that it will spend $470 million on a subterranean ice wall and other steps in a bid to stop leaks of radioactive water.

The Fukushima Dai-ichi plant has been leaking hundreds of tons of contaminated underground water into the sea since shortly after a massive 2011 earthquake and tsunami damaged the complex. Several leaks from tanks storing radioactive water in recent weeks have heightened the sense of crisis that the plant's owner, Tokyo Electric Power Co., isn't able to contain the problem.