Explosion at Japanese nuclear station following quake

A Japanese nuclear power plant has exploded, a day after a massive earthquake damaged the facility's cooling system. Residents have been warned to stay indoors.

Four people were injured in the explosion that occurred at the No. 1 reactor of the earthquake-struck Fukushima No. 1 nuclear power plant, Kyodo News reported.

The explosion followed large tremors and white smoke was seen at the facility, Tokyo Electric Power Company said.

Nuclear authorities had earlier warned that the Fukushima No 1 plant, located about 250km northeast of Tokyo, an urban area of 30 million people, "may be experiencing a nuclear meltdown".

The plant's cooling system was damaged in the quake that hit on Friday, leaving the government scrambling to fix the problem and evacuate more than 45,000 residents within a 10km radius.

Radiation levels inside the plant had increased 1000 times above the norm, although authorities said levels outside the facility's gates were only eight times above normal, which meant there was "no immediate health hazard''.

An official of the International Atomic Energy Agency (IAEA), the Vienna-based UN atom body, gave no further details.