Japan will accelerate efforts to prevent more radioactive groundwater from seeping into the ocean at the crippled Fukushima nuclear plant, government officials said on Wednesday, as critics slam its operator's handling of the issue.

Prime Minister Shinzo Abe is expected to order his government later in the day to hand over public money to help foot the bill for ramped-up measures, the first time that Tokyo has committed extra funds to deal with the growing problem.

"Taking measures to contain contaminated water is an important part of the process towards decommissioning (the site)," Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, told reporters.

"The prime minister is expected to instruct the industry minister to take measures as soon as possible."

In May, Tokyo ordered plant operator Tokyo Electric Power (TEPCO) to build new barriers around the plant's reactors to contain toxic water that is used to keep the reactors cool, a measure that could cost up to 40 billion yen.

There have been growing fears that existing safeguards will soon be overwhelmed by the highly radioactive water.

"As this large-scale construction of walls is unprecedented in the world, we think the government should take a step forward and support the plan," Suga said.

The vast utility is already facing staggering clean-up and compensation costs over the March 2011 accident, the worst atomic crisis in a generation.

Suga's comments come after Fukushima operator TEPCO last month admitted for the first time that radioactive groundwater had already leaked outside the nuclear plant, confirming long-held suspicions of ocean contamination from the shattered reactors.

The leaks have triggered alarm bells over the plant's precarious state and TEPCO's ability to deal with a long list of problems two years after it was swamped by a tsunami, sending reactors into meltdown.AFP