About two liters of radioactive water leaked from the turbine building of the second reactor at the crippled Fukushima Daiichi nuclear plant, Kyodo news agency reported on Sunday.
TEPCO, which operates the nuclear plant, issued a statement on Saturday saying the leak was from a pipe there that transfers highly radioactive water in the basement of the No. 2 reactor's turbine building to the plant's waste disposal facility.
The radiation level from the leak was low at 0.1 millisieverts per hour.
A level of radiation at 500 millisieverts per hour may cause cancer, while an acute radiation sickness begins with a dose of 1 sievert and chronic radiation sickness - from 1.5 sievert.
The company confirmed the water stopped leaking after it turned off the pump for the water transfer on the same day.
The contaminated water did not leak outside the nuclear plant, the company said.
A powerful earthquake and tsunami wrecked the Fukushima Nuclear Power Plant's cooling systems on March 11, 2011, causing meltdown at three of its reactors. Radiation leaked into the atmosphere, soil and seawater, causing the world's worst nuclear disaster since Chernobyl.
The Japanese Nuclear Safety Commission estimated the financial loss from the Fukushima Daiichi Nuclear Power Plant disaster at $74 billion. The dismantlement of four reactor tanks will cost $14.9 billion and $52 billion will be spent on compensation, clean-up of radioactive soil and other measures.