Workers trying to cool the reactor core to avoid a meltdown have been evacuated.

Earlier, Japan's nuclear agency said that levels of radioactive iodine in the sea near the plant had risen to 1,850 times the usual level.

It is believed the radiation at Fukushima is coming from one of the reactors, but a specific leak has not been identified.

Leaking water at reactor 2 has been measured at 1,000 millisieverts/hour - 10 million times higher than when the plant is operating normally.

The plant was damaged in the deadly 11 March earthquake and tsunami.

The death toll has now passed 10,000, and more than 17,440 people are missing.

The UN nuclear watchdog, the International Atomic Energy Agency (IAEA), has now sent extra teams to the Japanese nuclear plant.