The crippled nuclear plant at Fukushima is losing its two-year battle to contain radioactive water leaks and its owner emphasised for the first time it needs overseas expertise to help contain the disaster.
Tokyo Electric Power Co (Tepco) is grappling with the worst spill of contaminated water since the March 2011 earthquake and tsunami caused a meltdown at the Fukushima Dai-Ichi plant.
The call for help from Zengo Aizawa, a vice-president at the company, follows a leak of 300 tonnes of irradiated water.
Japan's nuclear regulator branded the incident "serious" and questioned Tepco's ability to deal with the crisis. Prime Minister Shinzo Abe made similar comments earlier this month.
Aizawa said: "We will revamp contaminated water management to tackle the issue at the Fukushima Dai-Ichi plant and seek expertise from within and outside of the country.
"There is much experience in decommissioning reactors outside of Japan. We need that knowledge and support."
The International Atomic Energy Agency and the US Nuclear Regulatory Commission said they were prepared to help.
Tepco said yesterday that it had found new radiation hotspots near tanks storing radioactive water, but no new leaks.
About 300 tonnes of toxic liquid is believed to have escaped from one of the tanks holding polluted water, some of which was used to cool broken reactors.
During inspections yesterday of about 300 other tanks, Tepco said while no more holes had been found, two areas were a cause for concern.
"We have confirmed two spots where radiation doses are high" near two other tanks, a company statement said.
Tepco was storing 330,000 tonnes of radioactive water as of last week in tanks covering an area equal to 37 football fields.
The company is clearing forest to make room for more tanks as it adds to the stored water at a rate of 400 tonnes a day.
The water is being pumped out from under the plant's reactors, which melted down as a result of the March 2011 earthquake and tsunami.
The water is treated to remove some of the cesium particles before it is stored, which has left 480 filters clogged with the radioactive material at the site.
Each weigh 15 tonnes and are warehoused in what the utility calls temporary storage, though it will take centuries to decay.
Other radioactive contaminants remain in the water even after treatment. That includes strontium, which has been linked to bone cancers.
Besides radiated water, the site north of Tokyo has more than 73,000 cubic metres of contaminated concrete, 58,000 cubic metres of irradiated trees and undergrowth and 157,710 gallons of toxic sludge, Tepco said.
Japan's nuclear watchdog has ratcheted up alarm over the potential for more leaks of highly radioactive water from the hundreds of storage tanks.
The possibility of leaks from other tanks "is the biggest concern," Nuclear Regulation Authority chairman Shunichi Tanaka said. "This will need to be handled carefully on the assumption that one incident could bring another."
Late on Wednesday night, Tepco said water leaking from the storage tank probably ran into the ocean, citing high radiation readings in a drainage ditch.
Up to 20 trillion becquerels of cesium and 10 trillion becquerels of strontium leaked into the sea since May 2011, said a company spokeswoman, which is about 100 times the annual limit.
Additional reporting by Agence France-Presse