TOKYO - Puddles with extremely high radiation levels have been found near water storage tanks at Japan's crippled Fukushima nuclear plant, its operator said Tuesday, as it moved to contain the latest of several toxic water threats.
The radiation level, measured around 50 centimetres (20 inches) above the toxic water surface, was about 100 millisieverts per hour, Tokyo Electric Power (TEPCO) said.
Scientists consider that level of radiation as harmful to human health.
An estimated 300 tonnes of water is believed to have leaked out from a huge radioactive water storage tank at the vast site, with the leak believed to be continuing Tuesday, TEPCO and the Nuclear Regulation Authority (NRA) said.
TEPCO denied that toxic water had flowed into the adjacent Pacific ocean, but the regulator ordered the utility to study the possibility that it had escaped through nearby drains.
The agency released a preliminary assessment that the situation amounted to a level one incident on an eight-point international scale from zero to seven - seven being the most serious reading.
"We have instructed TEPCO to find the source of contaminated water - from which tank the water is leaking - and to seal the leakage point," a regulatory official told AFP.
"We have also instructed them to retrieve contaminated soil to avoid a further expansion of toxic water, and to strengthen monitoring of the surrounding environment."