The operator of Japan’s crippled Fukushima nuclear plant says around 300 tonnes of highly contaminated water has leaked into the Pacific Ocean.
This comes after months of denial by the Tokyo Electric Power Company.
Japan’s Pacific neighbours, South Korea, demanded an explanation from the Japanese authorities.
Tepco general manager Masayuki Ono said: “We have discovered a radiation level strong enough to give someone a five year dose of radiation within one hour. We would like to apologise for the concern we have caused people.”
Tepco has come under fire from the Japanese government for its handling of the nuclear crisis.
Fukushima was wrecked by the earthquake and tsunami of March 2011.