Radioactive water may have leaked into the surrounding ground from a storage tank at Japan's Fukushima nuclear plant, Tokyo Electric Power Co (TEPCO) said Saturday, adding the incident underscores the safety concerns over the crippled nuclear fuel facility.

Apparently, close to 120 tons of radioactive water may have leaked from one of its seven underground storage tanks contaminating the ground operator said, adding that steps have been taken to prevent further leakage.

The company plans to pump 13,000 cubic meters of water remaining in the affected underground reservoir No. 2 to other vessels over the next two weeks.

"We are planning to transfer the water in the underground reservoir No.2 to the underground reservoir No.1 soon after it is ready," the TEPCO spokesman said in a statement.

The power company is yet to discover the cause of the leak in the storage tank that is used to store water that cools the plants reactors, a spokesman for the company, Masayuki Ono, said at a press briefing, Reuters reported.

The company did not specify how long the contaminated water had been leaking from the tank, but said it “assumed that there is no leakage to the ocean since there is no drainage ditch near the reservoir.” The leaking tank is located 800 meters away from the coast.

The leakage came after one of the systems keeping spent atomic fuel cool at the plant temporarily failed Friday, the second outage in a matter of weeks, AFP reported.

The nuclear facility was hit by one of the worst nuclear disaster since Chernobyl in March 2011 as a giant tsunami triggered by an earthquake of magnitude 9.0 destroyed back-up generators and crippled its cooling system leading the reactors into a meltdown. Nuclear reactors and the spent rods have to be kept cool after the use, to prevent it from overheating and melting down.

Work to decommission the plant is expected to take decades to complete.