Environmental campaign group Greenpeace has dismissed Japan's announcement as a 'smokescreen'. "By triumphantly declaring a cold shutdown, the Japanese authorities are clearly anxious to give the impression that the crisis has come to an end, which is clearly not the case," said Junichi Sato, executive director of Greenpeace Japan.

That left a small band of men - dubbed the Fukushima 50 - to try a series of ad hoc solutions, including the use of seawater to cool the melted fuel rods.

This then-contaminated cooling water subsequently became a major headache for TEPCO, which had to release tonnes of it into the Pacific, provoking the ire of fishermen as far away as China.

Swathes of this zone remain badly polluted, with the clean-up proceeding slowly amid warnings that some towns could be uninhabitable for three decades.

Waves up to 14 metres (45 feet) high swamped the reactors' cooling systems, sparking meltdowns, explosions and the release of radioactive material in the world's worst nuclear accident since Chernobyl in 1986.

The initial success of 'Step One' - the stable cooling of reactors and used fuel pools - was announced in July, after the quake-triggered tsunami pummelled the plant on March 11 and laid waste to much of the northeast coast.

Stabilisation of the reactors, whose molten cores spewed radioactive particles into the air and sea, marks the end of what the government has dubbed 'Step Two' of the nuclear clean-up.

In a live press conference, Prime Minister Yoshihiko Noda told the country the crippled reactors 'have reached a state of cold shutdown'.

Japan said on Friday it finally had control of leaking reactors at Fukushima, in what authorities say is a vital step on the long road to recovery, nine months after its nuclear crisis began.