Japan's nuclear safety regulators have told the operator of a nuclear power plant in the area hit by a powerful New Year's Day quake to study its potential impact.

The Nuclear Regulation Authority (NRA) asked for further investigation even though initial assessments showed the Shika nuclear power plant's cooling systems and ability to contain radiation remained intact.

The order reflects Japan's greater vigilance about safety risks after meltdowns in 2011 at a plant in Fukushima, on the northeastern Pacific coast, following a magnitude-9 quake and a massive tsunami.

The January 1 magnitude-7.6 quake and dozens of strong aftershocks have left 206 people dead and dozens more unaccounted for. It also caused a small tsunami. But Hokuriku Electric Power Co., the plant's operator, reported it had successfully dealt with damage to transformers, temporary outages and sloshing of spent fuel cooling pools that followed the quakes.

Chief Cabinet Secretary Yoshimasa Hayashi emphasized that the plant was safe. Eighteen of 116 radiation monitoring posts installed in Ishikawa prefecture, where Shika is located, and in neighboring Toyama, briefly failed after the quake. All but two have since been repaired, and none showed any abnormality, he said.

Shika is a town on the western coast of the Noto peninsula, where the quake did the most damage, leaving roads gaping, toppling and collapsing buildings and triggering landslides.

Hokuriku Electric reported that water had spilled from the spent fuel pools in both reactors. Transformers in both reactors were damaged and leaked oil, causing a temporary loss of power in one of the cooling pools. Company officials reported no further safety problems at the NRA's weekly meeting on Wednesday.

But NRA officials said the utility should consider the possibility of fresh damage to transformers and other key equipment as aftershocks continue.

NRA chairperson Shinsuke Yamanaka urged the utility to thoroughly investigate the cause of the transformer damage and promptly report its findings. They also were instructed to study if earthquake responses at the plant should be reevaluated.

The Shika reactors were inaugurated in 1993 and 2006. They have been offline since the 2011 disaster.