The operator of the crippled Fukushima nuclear plant says it has found a new leak of radioactive water that might have flowed into the Pacific Ocean.

The leak from the 450-tonne storage tank is the second of its kind in as many months, and involved water with high concentrations of radioactive strontium and caesium.

Fukashima operator Tokyo Electric Power (TEPCO) says it does not know how much water leaked, adding that it could have flowed from an adjoining drainage ditch into the sea.

TEPCO has apologised for causing anxiety.

Last month, 300 tonnes of highly contaminated water leaked from a tank and some is believed to have flowed into the Pacific.

TEPCO has been relying on hastily-built tanks to hold excess cooling water flushed over damaged reactors at the Fukushima Daiichi site, where three units suffered nuclear meltdowns and hydrogen explosions after a March 2011 earthquake and tsunami.

TEPCO has been pumping hundreds of tonnes of water a day over the Fukushima reactors to keep them cool and storing the radioactive wastewater in tanks above ground.

It has also found high levels of radiation just above the ground near other tanks, suggesting widespread structural problems with the tanks.

Recent mishaps at the site have returned TEPCO to the spotlight and called into question its ability to carry out a complex cleanup that is widely expected to take decades.

Amid mounting international alarm, Japan’s government stepped in and said it will fund efforts to improvement water management at the plant.

ABC/Reuters