Obayashi TOKYO: Contaminated water with dangerously high levels of radiation is leaking from a storage tank at Japan’s crippled Fukushima nuclear plant, the most serious setback to the clean up of the worst nuclear accident since Chernobyl.

The storage tank breach of about 300 tonnes of water is separate from contaminated water leaks reported in recent weeks, plant operator Tokyo Electric Power Co said on Tuesday.

The latest leak, which is continuing, is so contaminated that a person standing 50 centimetres (1.6 feet) away would, within an hour, receive a radiation dose five times the average annual global limit for nuclear workers.

After 10 hours, a worker in that proximity to the leak would develop radiation sickness with symptoms including nausea and a drop in white blood cells.

“That is a huge amount of radiation. The situation is getting worse,” said Michiaki Furukawa, who is professor emeritus at Nagoya University and a nuclear chemist.

The embattled utility Tokyo Electric has struggled to keep the Fukushima site under control since an earthquake and tsunami caused three reactor meltdowns in March 2011.

Japan’s Nuclear Regulation Authority has classified the latest leak as a level 1 incident, the second lowest on an international scale for radiological releases, a spokesman told Reuters today.

But it is the first time Japan has issued a so-called INES rating for Fukushima since the meltdowns. Following the quake and tsunami, Fukushima was assigned the highest rating of 7, when it was hit by explosions after a loss of power and cooling.

and we need to review not only the tanks but also our monitoring system,” he said.

Continued contaminated water leaks from Fukushima has alarmed Japan’s neighbours South Korea and China.

Tokyo Electric, also known as Tepco, has been criticised

for its failure to prepare for the disaster and been accused of covering up the extent of the problems at the plant.