An estimated 300 tons of radiation-contaminated water is flowing into the Pacific Ocean daily from a crippled Japanese nuclear power plant, the government said on Wednesday.

In July, the operator, Tokyo Electric Power Co, admitted that radioactive water at the Fukushima Daiichi Nuclear Power Station had seeped into the ground and contaminated the sea. But they did not know what caused the leak.

The plant suffered meltdowns at three of its six reactors after a tsunami swept through the complex in March 2011.