The deepening crisis at the Fukushima nuclear plant in Japan will be upgraded from a level 1 "anomaly" to a level three "serious incident" a spokesman for Japan's Nuclear Regulation Authority said today.
Japan's nuclear watchdog said it is concerned that more storage tanks at the wrecked Fukushima nuclear plant will spring leaks, following the discovery that highly contaminated water is leaking from one of the hastily built containers.
Water still leaking from the plant is so contaminated that a person standing close to it for an hour would receive five times the annual recommended limit for nuclear workers in a year.
A maximum level 7 was declared at the battered plant after explosions led to a loss of power and cooling two years ago, confirming Fukushima as the worst nuclear accident since Chernobyl a quarter of a century earlier.
Contaminated water with dangerously high levels of radiation is leaking from a storage tank at Fukushima, the plant's operator, Tokyo Electric Power Co said on Tuesday. The leak was classified as an "anomaly" earlier this week.
"Judging from the amount and the density of the radiation in the contaminated water that leaked ... a level 3 assessment is appropriate," the document said.
The leak, which has not been plugged, is so contaminated that a person standing 50 cm (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.
Each one-step INES increase represents a tenfold increase in severity, according to a factsheet on the website of the International Atomic Energy Agency.
Earlier this year, Japan marked the second anniversary of the devastating earthquake and tsunami which left nearly 19,000 people dead or missing and hundreds of thousands of people still displaced.
The magnitude 9.0 earthquake hit on March 11 2011 - the strongest recorded in Japan's history.
Japan has struggled to clean up radiation from the Fukushima Dai-Ichi nuclear plant, whose reactors melted down after its cooling systems were disabled by the tsunami, and rebuild lost communities along the coast.
Throughout the disaster zone, tens of thousands of survivors are living in temporary housing and are impatient to get resettled, a process which could take up to a decade, officials say.
Further south, in Fukushima prefecture, some 160,000 evacuees are uncertain if they will ever be able to return to abandoned homes around the Fukushima Dai-ichi nuclear power plant, where three reactors melted down and spewed radiation into the surrounding soil and water after the tsunami knocked out the plant's vital cooling system.
The disaster was the worst since Chernobyl in 1986.