Workers at Japan’s crippled Fukushima nuclear plant have spilled four tonnes of radioactive water, likely contaminating the soil and possibly groundwater.
A spokesman for the plant’s operator Tokyo Electric Power (TEPCO) said the accident occurred during the transfer of polluted rain water from one of the plant's concrete gutters to an empty storage tank.
TEPCO has estimated roughly four tonnes of collected rainwater might have escaped.
The spokesman said the extent of contamination was unclear although it was not thought to be highly polluted.
"The water itself was rain water. But it was from the Fukushima Daiichi nuclear plant and could contain radioactive materials," he said.
"The water seeped into the ground."
TEPCO has long struggled to control waste water at the plant.
The company poured thousands of tonnes of water onto runaway reactors to keep them cool, and continues to douse them.
TEPCO has so far disclosed no clear plan for disposing of the huge amounts of stored polluted water, which is stored at hundreds of tanks at the plant.
Some tanks have leaked highly radioactive waste water, which might have washed to sea.
All of Japan's 50 reactors were shut down after the 2011 earthquake and tsunami crippled the Fukushima plant, triggering a nuclear crisis and a spike in popular opposition to the industry.