The operator of the Shika nuclear power plant in central Japan has shown its damaged equipment to media for the first time since it was hit by a massive earthquake on New Year's Day.

Officials of Hokuriku Electric Power Company invited reporters to the nuclear plant in Ishikawa Prefecture on Thursday.

The plant experienced a tremor equivalent to an intensity of upper 5 on the Japanese seismic scale of 0 to 7 in the second basement floor of the No.1 reactor building.

The quake reportedly damaged piping and other parts of a transformer for the No.2 reactor, causing about 19,800 liters of oil to leak with some spilling into the sea. The damage has left two out of five power cables unusable.

Hokuriku Electric Power said repair work is underway, but the company has not set a timeline for the restoration as it is carrying out further inspections.

But the utility said electricity supply for the spent fuel pools and other key facilities are secure as it has emergency generators and other power sources.

Company officials also showed to media the No.1 reactor's transformer damaged by the quake. They explained that the equipment was temporarily restored last month.

The nuclear plant has encountered a series of problems since the major earthquake. One of its six emergency diesel generators automatically stopped during a test-run.

The company's senior official, Nakata Mutsuhiro, said the operator revised information for the public repeatedly amid the confusion after the disaster. An initial response was a serious challenge for the utility.

He added that efforts need to be made to sort out problems and conduct training to improve its disaster response.

The two reactors have been offline since 2011. The No.2 reactor is currently undergoing inspections for the restart.

But the process is expected to take years as the country's nuclear regulator plans to reflect additional findings, such as the mechanism of the latest quake and its geological fault activity.