Japan on Friday looked set to announce it had finally tamed leaking atomic reactors at the Fukushima Daiichi power station, nine months after one of the world's worst nuclear crises began.

Prime Minister Yoshihiko Noda was expected to tell a disaster-weary public that all reactors at the plant were in a state of cold shutdown.

The government and plant operator Tokyo Electric Power (TEPCO) have long targeted the year's end for the milestone.

The announcement will be followed by fresh steps towards decommissioning the reactors, a process that is expected to take more than three decades.

The Fukushima Daiichi nuclear plant was severely damaged by the 9.0-magnitude earthquake and resulting tsunami that smashed into Japan on March 11.

Waves up to 14 metres (46 feet) high swamped the reactors' cooling systems, sparking meltdowns, explosions and the release of huge amounts of radioactive materials -- the world's worst nuclear accident since Chernobyl in 1986.

TEPCO was caught short by the disaster, with its tsunami defence systems overwhelmed and back-up power generators knocked offline, leaving a small band of men -- dubbed the Fukushima 50 -- to try a series of jerry-rigged solutions, including the use of seawater to cool the melted fuel rods.

Water used in the cooling process subsequently became a major headache for TEPCO, which had to release tonnes of the contaminated liquid into the Pacific, provoking the ire of local fishermen.

Farmers in the area also suffered, with produce shunned by consumers or banned by the government because of radioactive contamination.

An exclusion zone around the plant was established with tens of thousands of people evacuated to avoid them being exposed to dangerously high levels of radiation.

Swathes of this zone remain polluted, with the clean-up plodding along amid warnings that some towns could remain uninhabitable for decades.

The hoped-for end to the disaster looked like it had suffered a set-back earlier this month, when TEPCO said its latest calculations showed the fuel inside the No. 1 reactor could have melted entirely, dropping through its inner casing and eroding a concrete base.

In the worst-case scenario, the molten fuel could have reached as far as 65 centimetres (2 feet) into the concrete, leaving it only 37 centimetres short of the outer steel casing.

TEPCO has also said that it believed 150 litres (40 US gallons) of waste water including highly harmful strontium, a substance linked to bone cancers, has found its way into the open ocean.

While the natural disaster claimed 20,000 lives, the nuclear emergency has recorded no direct casualties, but it has badly dented the reputation of a technology on which Japan previously depended for a third of its electricity.