A spokesman for Tokyo Electric Power said the level of radiation found in the leaked water was 10 million times higher than it should be for water inside the reactor, indicating damage to the fuel rods.

"We detected 1,000 millisieverts per hour of radiation in a puddle of water at the reactor number two. This figure is 10 million times higher than water usually kept in a reactor," the spokesman said.

"We are examining the cause of this, but no work is being done there because of the high level of radiation.

"High levels of caesium and other substances are being detected, which usually should not be found in reactor water. There is a high possibility that fuel rods are being damaged."