Japan raises spectre of Fukushima 'melt-through'

For the first time, Japanese authorities have suggested the situation at the Fukushima nuclear plant may have gone beyond a meltdown.

An official report, which Japan will submit to the UN's nuclear watchdog, says nuclear fuel in three reactors at Fukushima has possibly melted through the pressure vessels and accumulated in outer containment vessels.

Japan's Yomiuri Shimbun newspaper says this "melt-through" is far worse than a core meltdown, and is the worst possibility in a nuclear accident.

This is the first official admission that a "melt-through" may have occurred.

In the report, Japan also admits it was unprepared for the scale of the Fukushima disaster, which struck after a devastating earthquake and tsunami in March.

The report also acknowledges there was insufficient communication between the government and the plant's operator.