An aerial view shows the quake-damaged Fukushima nuclear power plant in the Japanese town of Futaba, Fukushima prefecture in March 2011. Japan's prime minister said the decommissioning of the crippled Fukushima nuclear plant would take decades, in the first government announcement of a long-term timeframe for the clean-up.

Japan's prime minister said on Saturday the decommissioning of the crippled Fukushima nuclear plant would take decades, in the first government announcement of a long-term timeframe for the clean-up.

A monster tsunami crippled cooling systems at the Fukushima Daiichi plant following the March 11 earthquake, with three reactors suffering meltdowns, triggering the world's worst in a generation.

"Many people have been forced to evacuate," Naoto Kan said during a meeting of the ruling Democratic Party of Japan.

"It is expected to take three, five, or 10 years for controlling it, and even several decades until the accident settles finally."

The Japan Atomic Energy Commission and Fukushima plant operator Power Co have set a provisional goal of starting the removal of melted nuclear fuel at about 2021, NHK said.

The station reported that the authorities, the operator and equipment manufacturers also expect "several decades" to pass before the reactors are ready to be dismantled, citing a long-term roadmap for bringing the plant under control.

Japan has unveiled a short-term to stabilise the Fukushima Daiichi nuclear plant, which has emitted high levels of radiation after its cooling systems were knocked out.

But the government had not until Saturday presented an estimate of how long it will take before the crisis can be brought to an end.

The blueprint obtained by NHK was mapped out by studying how the United States handled the 1979 Three Mile nuclear accident, the broadcaster said.

TEPCO expects to reduce by July and bring its reactors to a stable cold shutdown by January at the latest.

Goshi Hosono, newly appointed state minister in charge of handling the , has told Jiji Press that the government will announce a revised roadmap and a longer-term vision for the accident on July 19.