A TEPCO worker checks contamination around a water tank at Fukushima on September 4, 2013. Japan has pledged a renewed push to contain potentially hazardous leaks.

Japan pledged a renewed push to contain potentially hazardous leaks at Fukushima on Tuesday after the operator of the crippled plant reported spiking levels of radiation in groundwater.

Late on Monday, two days after Tokyo won the bid to host the 2020 Olympics, plant operator TEPCO announced samples taken from a well at the site showed the presence of radioactive substances, including strontium, a known carcinogen.

Reports said the utility believed it "now seems more likely" that leaks from tanks storing highly polluted water had made their way into subterranean water, which flows out to sea.

In a release, Tokyo Electric Power (TEPCO) said groundwater showedthe plant and its waste water crisis, Chief Cabinet Secretary Yoshihide Suga said.

"We will consider ways to utilise the knowledge of people in and out of Japan... and to enhance our international communication on the waste water issue," Suga told reporters.

Thousands of tonnes of radioactive water are being stored in temporary tanks at Fukushima. Much of it has been used to cool molten reactors at the plant wrecked by the earthquake and tsunami of March 2011.

TEPCO and Japanese officials are considering releasing some of it into the Pacific Ocean after filtering out radioactive materials, but face opposition from fisherman and neighbouring countries.

The operator said last month that around 300 tonnes of mildly polluted water is running into the Pacific Ocean every day as a result of groundwater flowing