Tokyo, Aug 21 (IANS): Some 300 tonnes of highly-contaminated water that leaked from a storage tank at the Fukushima Daiichi nuclear power plant may be removed later Wednesday, Tokyo Electric Power Co. (TEPCO) has said.

The company reported the leak Tuesday, which led the country's Nuclear Regulation Authority to consider raising the severity assessment of the event to level three from the initial level one, Xinhua reported.

Level three on the International Nuclear and Radiological Event scale is defined as a "serious incident".

TEPCO is currently transferring water from the tank to other tanks nearby. The utility confirmed it will be safe, adding the tanks are of the same type.

TEPCO found the leakage Monday as water level in one of the tanks was lowered by about 2.9 metres. The 11-metre-high tank contained about 1,000 tonnes of water before and an estimated 300 tonnes of water is thought to have leaked.

The company detected about 80 million becquerels per litre of radioactive substances emitting beta ray, such as strontium-90.

The plant has struggled with a series of radioactive water leaks and power failures since March 2011 when an earthquake-triggered tsunami destroyed its power and cooling systems, causing multiple meltdowns.

The storage tanks were built around the plant to store radioactive water leaked from the reactors.