The embattled nation, reeling from the triple calamity of a massive earthquake, tsunami and a crippled atomic power plant, was also inviting foreign experts to help stabilise the overheating Fukushima station.

The United States has lent Japan robots of a model battle-tested in Iraq and Afghanistan that can crawl through, film and clear rubble in the blast-hit reactor buildings which humans can't enter because of very high radiation.

And France, which relies on nuclear power for three-quarters of its domestic energy needs, was sending an expert team from Areva, its state-run reactor maker, to assist embattled operator Tokyo Electric Power Company (TEPCO).

The strain of the crisis appeared to have taken a toll on TEPCO's president Masataka Shimizu, 66, who was hospitalized Tuesday evening with high blood pressure and dizziness, having not appeared in public for over two weeks.

AFP