The grip of the nuclear lobby in Japan before the Fukushima disaster was akin to that of the military in the run up to World War II, the prime minister at the time of last year's catastrophe said Monday.

At a parliamentary inquiry into the world's worst atomic crisis in 25 years, Naoto Kan said the lion's share of the blame for the tsunami-triggered disaster lay with the state for its unquestioning promotion of nuclear power.

"The nuclear accident was caused by a nuclear plant which operated as national policy," Kan said.

"I believe the biggest portion of blame lies with the state," said the former premier, who has come out strongly against the technology since the Fukushima disaster in March last year.

But, he said, the "nuclear village" -- a term critics often use to refer to the pro-atomic lobby of academics and power companies -- had blinded the government in a way analogous to the rise of the powerful military elite that led Japan into the vicious colonialism that precipitated World War II.

"Before the war, the military came to have a grip on actual political power... (Similarly, plant operator) TEPCO and FEPC (Federation of Electric Power Companies of Japan) held sway over the nation's nuclear administration over the past 40 years," Kan said.

"They ousted experts, politicians and bureaucrats critical of nuclear energy from the mainstream. Many others they sidelined so that they could maintain the status quo."

Kan, who stepped down in September after just 15 months in charge, said the only way to ensure that a disaster like Fukushima did not happen again was for Japan to abandon nuclear technology.

Kan's appearance, like that of many former ministers called to give evidence before the panel, was an opportunity for the ex-premier to give a detailed public account of his actions in the days and weeks after the tsunami struck.

Kan came in for intense criticism for creating a distraction when he visited the Fukushima Daiichi nuclear plant the day after the waves hit, as emergency workers were grappling with what would become full-blown meltdowns.

His administration was also lambasted for providing too little information to the public, apparently withholding computer models that showed how radiation from the venting reactors might spread.

Tens of thousands of people were later evacuated from an area around the plant after it began spewing radiation. Many have still not been allowed home, with some areas expected to be uninhabitable for decades.

TEPCO, one of the world's largest utilities, whose tentacles of influence reach well inside Japan's huge government bureaucracy, has also been criticised for ignoring warnings about the potential dangers from quake-generated tsunamis.

At the hearing Monday, Kan attacked the company for its failure to keep the government informed about the accident.

"I was thinking it was a battle against an invisible enemy," he told the hearing.

Kan's public testimony came after a private panel probing the accident said in February the former premier's aggressive involvement had averted a worse crisis.

That panel said it was Kan who ordered TEPCO, which refused to co-operate with the February study, to keep men on site.

Experts concluded that if the premier had not stuck to his guns, Fukushima would have spiralled further out of control, with catastrophic consequences.

Kan's then-top government spokesman, Yukio Edano, testified on Sunday.

Asked about Kan's visit to the Fukushima plant, Edano said the prime minister had gone to the site because the industry watchdog Nuclear and Industrial Safety Agency and TEPCO had seemingly "backtracked and wavered".

"We had this awareness that someone who is more important than a vice industry minister (who was already at the scene) should go and take hold of the situation," Edano said.