TOKYO - Japan's tsunami-stricken Fukushima nuclear power plant has reached cold shutdown, Prime Minister Yoshihiko Noda said on Friday, a key milestone in efforts to bring under control the world's worst nuclear accident since Chernobyl 25 years ago.

"Even if unforeseeable incidents happen, the situation is such that radiation levels on the boundary of the plant can now be maintained at a low level," Noda said at the government's nuclear emergency response meeting.

The Fukushima Daiichi plant, 240 km (150 miles) northeast of Tokyo, was wrecked on March 11 by a huge earthquake and a tsunami that exceeded 15 metres (45 feet) in some areas, which knocked out its cooling systems, triggering meltdowns and radiation leaks.

Declaring a cold shutdown will have repercussions well beyond the plant: it is a government pre-condition before it allows about 80,000 residents evacuated from within a 20 km (12 mile) radius of the plant to return home.