The operator of the Shika nuclear power plant in central Japan's Ishikawa Prefecture says it may take more than six months to finish repairing the damage caused by the massive New Year's Day earthquake.

Hokuriku Electric Power Company has disclosed that the quake damaged transformers used to supply power to the plant from outside, and that two of five power cables have become unusable. The plant's two reactors have been offline since 2011.

The operator says electricity supply for the spent fuel pools and other important facilities is secure as it has emergency diesel generators and power supply vehicles that can be used even when the plant cannot receive electricity from outside.

The company also says larger-than-expected tremors hit the plant's foundation, but since the jolts lasted a relatively short cycle of 0.47 seconds, they didn't have a major impact on key structures, such as reactor containment vessels and reactor buildings.

The operator has also disclosed that tsunamis measuring up to 3-meters high reached the site several times and a backwash caused the seawater surface to recede by one meter.

The company says the waves did not cause safety problems at the plant, which is built 11 meters above sea level and has a 4-meter-tall seawall. Its water intake for cooling facilities is 6.5 meters below sea level.

The plant has experienced additional trouble after the quake. When the operator conducted a test-run of five emergency generators last Wednesday, one of them stopped automatically.

The Nuclear Regulation Authority has asked the operator to repair the damaged transformers and emergency generator swiftly, as well as to look into the cause of the trouble.