Japanese nuclear regulators and power companies have a history of underestimating the danger posed by active faults near a number of reactors, a scientist says.

Toyo University Professor Mitsuhisa Watanabe, who has long sounded the alarm about active faults under and near nuclear power plants, has been named to an expert panel investigating possible active faults beneath the Oi nuclear plant in Fukui Prefecture, a study that may impact all of Japan's currently offline reactors.

Watanabe maintains that a potentially dangerous active fault runs directly beneath critical equipment for Oi's number 3 and 4 units, the only two commercial reactors in Japan currently operating.

He has called for the immediate shutdown of the plant until thorough geological surveys can be conducted, The Japan Times reported Thursday.

Watanabe is critical of seismic experts in the pay of the nuclear power industry for playing down the risk of earthquakes and tsunamis before the March 2011 disaster at the Fukushima No. 1 power plant.

"The nuclear regulator and power companies have long tried to underestimate [the danger] of active faults, worrying it would affect power supply capacity," he said.

"We should not repeat the same mistake that was made in Fukushima."