Prime Minister Yoshihiko Noda made the announcement at a nuclear task-force meeting.

Declaring a cold shutdown condition is seen as a key milestone in efforts to bring the plant under control.

But the government says it will take decades to dismantle it completely.

The six-reactor Fukushima Daiichi nuclear plant was badly damaged by the March 11 earthquake and tsunami. Blasts occurred at four of the reactors after waves knocked out vital cooling systems.

Workers at the plant, which is operated by Tokyo Electric Power Company (Tepco), have been using sea water to cool the reactors. Waste water has built up and some contaminated liquid has been released into the sea.