Tokyo Electric Power Co. said radioactive water was spilling from a storage tank at the Fukushima nuclear power plant. It's the first acknowledgement of an incident of its kind since a magnitude-9 earthquake triggered a meltdown at the facility in 2011.
The Wall Street Journal reported 79,000 gallons of radioactive water leaked from the tank. The Japanese government said contaminated groundwater was flowing from the complex, near the Pacific Ocean.
Greenpeace said it was concerned about Tepco's ability to monitor the status of the nuclear facility.
"An urgent appeal for international assistance must be made immediately," the group said in a Tuesday blog post. "This is an emergency none of us can afford to ignore."
Tepco said Monday two workers were contaminated with radioactive material at the nuclear power plant. The company said the level of contamination was low, the workers were cleaned and later released.