Japan nuclear crisis: 'Maybe the worst is not yet behind us'

The former head of the International Atomic Energy Agency has warned that the worst may not be over for Japan.

The warning comes after the Fukushima Daiichi nuclear plant was rocked by a third blast, which appears to have damaged one of the reactors' containment systems for the first time.

The Japanese government now says radiation levels have fallen at the nuclear plant following a spike that reached harmful levels.

Ollie Heinonen said the worst possible scenario would be a core meltdown at the plant.