Japan's former prime minister says he feared early in the March nuclear crisis that it might become many times worse than the Chornobyl disaster and threaten the country's survival.

Naoto Kan says now he imagined "deserted scenes of Tokyo without a single man" and the need to evacuate tens of millions of people.

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Former prime minister Naoto Kan, who resigned last week, says he thought early in the March nuclear crisis that it might threaten Japan's survival. (Koji Sasahara/AP Photo)

"It was truly a spine-chilling thought," Kan said in an interview with the Tokyo Shimbun daily published Wednesday.

Kan said those images flashed in his mind during the first week of the crisis, when information coming from the radiation-leaking Fukushima Dai-ichi plant was sketchy and he was told that its operator, Tokyo Electric Power Co., was considering pulling out its staff. TEPCO has since said that it never planned to withdraw from the plant.

Kan, who resigned last week amid criticism over his administration's handling of the disaster, said when he heard that cooling systems had failed at the nuclear plant soon after it was damaged by a March 11 tsunami, he understood the gravity of the situation.

"The power was totally lost and there was no cooling capacity. I knew what that meant. So I thought, 'This is going to be a disaster."'

Much worse than initial report

Kan said crisis management at the plant failed because the emergency plans included no scenario for a total power failure.

Authorities have since said that the cores of three of the six reactors melted down — much worse than they said initially — spewing about one-sixth the radiation emitted by the accident at Chornobyl.

In Madrid Wednesday, crews in Japan that worked to bring the damaged Fukushima Dai-ichi nuclear plant under control after won a Prince of Asturias humanitarian award, the foundation behind the prize said.

The foundation said the crews had risked their lives to save others by struggling to keep the radiation disaster from spreading.

It singled out three specific groups of workers: employees of the TEPCO company that operated the plant, firefighters that worked to keep the plant cool, and armed forces personnel who used helicopters to splash the plant with water, inspect it from the air, cordon off an exclusion zone or evacuate people.

'Withdrawing from the plant was out of the question. If that had happened, Tokyo would have been deserted by now.' —Former Japan PM Naoto Kan

The statement said that those involved represent "the highest values of the human condition."

Kan said he heard from then-trade minister Banri Kaieda after a series of hydrogen explosions that TEPCO was considering pulling out staff from the nuclear plant.

Without staff to cool the overheated reactors, Kan said he knew the reactors and spent nuclear fuel stored in pools would "rapidly melt down and release massive amounts of radiation."

He said he summoned then-TEPCO president Masataka Shimizu for an explanation, but he "never told me anything clearly."

"Withdrawing from the plant was out of the question. If that had happened, Tokyo would have been deserted by now. It was a critical moment for Japan's survival. It could have been a disaster leaking dozens of times more radiation than Chornobyl," he said.

"Japan was facing the possibility of a collapse" at that time, he said in a separate interview published Wednesday by the Mainichi newspaper. "I was under an enormous sense of crisis."

The Fukushima complex is about 225 kilometres northeast of Tokyo. The greater Tokyo area has more than 30 million people.

Some 100,000 people from around the plant have been evacuated. While the amount of radiation leaking from the plant has dropped significantly, authorities say accumulated radiation in the soil and vegetation may make it difficult for residents to return to their homes for some time, perhaps years.