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 11 March 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.
A 20km (12m) exclusion zone remains in place around the plant.
The Japanese government said earlier this year that it was aiming to reach a “cold shutdown condition” at the plant by the end of the year.
This is where water that cools nuclear fuel rods remains below boiling point, meaning that the fuel cannot reheat.
More than 80,000 people had to leave the area, but radiation levels in some places remain too high for them to return home.
Contamination has been found in foodstuffs from the region including rice, beef and fish, while radioactive soil has also been found in some areas.