The Fukushima number one power plant is the hardest hit so far. There was a hydrogen explosion on Monday morning at the plant's number three reactor. The blast was felt at least 40km away.

A similar explosion happened at the same plant on Saturday, but at the Number One reactor. Workers were injured but no damage was reported to the container holding the reactor's radioactive core.

And a state of emergency had been declared at the Onagawa plant - although officials say radioactivity levels have now returned to normal standards.

As the prospect of a nuclear disaster looms, Japan's government says it's doing all it can to mitigate the crisis.

Al Jazeera's Florence Looi reports.