An estimated 360 liters of radioactive water has leaked from a desalination unit at the ruined Fukushima No. 1 nuclear power plant, Tokyo Electric Power Co. said Friday.

The utility said water did not leave the complex but did not disclose its radiation level.

The leak was discovered after a leak detector went off at around 3 a.m. Friday. A plant worker found the water in a building housing the desalination unit and suspended it.

The desalination unit is used to remove salt from radioactive water after cesium and other radioactive materials have been filtered out.