Japan's prime minister was due Thursday to tour the crippled Fukushima nuclear plant less than two weeks after he assured the world it was "under control" -- despite huge problems at the site.

The pledge by Shinzo Abe was seen as key to Tokyo's successful bid to host the 2020 Olympic Games.

His visit comes as it emerged that just months after the March 2011 disaster, authorities allowed operator Tokyo Electric Power (TEPCO) to shelve plans to deal with groundwater over fears it would push the massive utility into bankruptcy.

Hundreds of tonnes of groundwater are becoming contaminated daily as it mixes with highly polluted water used to cool the broken reactors. The water then flows out to sea.

Abe arrived at TEPCO's disaster headquarters, which lie just outside an exclusion zone thrown up around the plant, Thursday morning and was due to arrive at Fukushima Daiichi, some 220 kilometres (140 miles) north of Tokyo, around noon, officials said.

The premier was expected to don a protective suit before he inspects work being carried out on tanks storing contaminated water, as well as that on decontamination systems.

He will also meet staff working to clean up the worst nuclear disaster in a quarter of a century.

The visit is part of a public relations campaign aimed at reassuring the world about the state of the plant, more than two-and-a-half years after it was thumped by a huge tsunami.

Speaking to Olympic chiefs in Buenos Aires just ahead of a decision to award the Games to Tokyo, Abe said of the plant: "Let me assure you, the situation is under control."

But some critics and experts say Abe's gloss on the disaster is bordering on the dishonest -- a senior TEPCO executive flatly contradicted the PM earlier this month.

"I think the current situation is that it is not under control," he told opposition lawmakers.

TEPCO has poured thousands of tonnes of water on the Fukushima reactors to tame meltdowns sparked by the March 2011 earthquake and tsunami.

The utility says they are now stable but need to be kept cool to prevent them running out of control again.

Much of that now-contaminated water is being stored in temporary tanks at the plant, and TEPCO has so far revealed no clear plan for it.

The problem has been worsened by leaks in some of those tanks that are believed to have seeped into groundwater.

TEPCO has come under fresh pressure after the opposition Democratic Party of Japan (DPJ), which governed the nation when the crisis occurred, admitted having acceded to the utility's request to shelve plans for a costly underground barrier to halt this flow.

Sumio Mabuchi, a DPJ lawmaker who was then in charge of the disaster management, told a party committee on Wednesday that the government shared concerns that the construction would plunge the utility deeper into debt and could force it into bankruptcy.

The revelations will add to the impression that TEPCO is more concerned with its bottom line than with fixing the mess at its leaking plant.