A crack in the concrete catchment of a desalination facility of the Fukushima Daiichi Nuclear Power Station has leaked 45 tons of highly radioactive water, according to TEPCO, operator of the plant.

TEPCO said Sunday some of the water may have leaked into the Pacific Ocean.

The leak was noticed when a catchment was flooded and water escaped from a crack reaching an external drainage ditch.

The water has up to one million times as much radioactive strontium as the maximum safe level. It also contains about 300 times the safe level of radioactive cesium. Strontium is easily absorbed by living tissue and can cause cancer.

TEPCO said measures are being taken to stop the leak and determine if contaminated water had reached the ocean.

The plant was damaged and crippled when a magnitude 9 earthquake struck northeastern Japan in March followed by a tsunami. In May, nearly 60 tons of radioactive water leaked from the plant's wastewater storage facility.

Radioactive leakage to the ocean contaminates marine life, including seafood posing health risk to human. The environmental group Greenpeace measured radioactivity level in waters 19 kilometres off the coast of the nuclear power plant in May and found high levels of radioactive iodine and radioactive cesium in fish, shellfish, and seaweed samples.