Workers have restored power to cooling systems at two of the six reactors at Japan's quake-damaged Fukushima Daiichi nuclear plant, the NHK television reported.

A cooling pump at reactor 5 and an emergency diesel generator at reactor 6 have "resumed operations," Japan's Nuclear and Industrial Safety Agency told a news conference on Saturday.

Firefighters are desperately trying to cool the overheated nuclear cores in an attempt to avert a meltdown.

The crisis was prompted by last week's 9.0-magnitude earthquake and tsunami that killed thousands.

The confirmed death toll now stands at just under 7,200, while about 11,000 remain missing.