A stunned Japanese cabinet felt no one was taking charge days after a tsunami smashed into the Fukushima nuclear power plant, unofficial minutes released on Friday showed, evidence of the scale of confusion as the country faced its biggest crisis since World War Two.

Ministers also thought there might be a meltdown just hours after the disaster struck on March 11 last year, but they gave no sign to the public of their worst fears.

The chaotic response and revelations that officials had withheld information have deepened distrust of politicians and bureaucrats, and public indignation at their incompetence.

Then-premier Naoto Kan and his staff began referring to a worst-case scenario that could threaten Japan's existence as a nation around three days after the earthquake and tsunami, according to the report by a panel set up by a private think-tank.

The disaster knocked out cooling systems at Tokyo Electric Power Co's (Tepco) Fukushima Daiichi plant, triggering the world's worst nuclear accident since Chernobyl in 1986.

Who is the leader of the actual operation? Yoshihiro Katayama, internal affairs minister at the time, asked at a March 15 meeting of the Nuclear Emergency Response headquarters.

I've got too many unintelligible demands and requests. No one is holding the reins.

A day earlier, Kan spoke of a consensus among specialists that a 20-km (12-mile) evacuation zone around the plant was sufficient. He was challenged by Koichiro Gemba, national strategy minister at the time, who pointed out contradicting views.

POSSIBILITY OF MELTDOWN FORESEEN

This is war, Gemba told a different meeting. We only win or lose. We are already losing in some battles. But the important thing is how we manage to limit our loss.

The minutes, put together from participants' memos, recordings and memories since no official records were kept, were released two days before the first anniversary of the disaster that left 19,000 dead or missing.

Health worries have dogged the Japanese public ever since March 11 with excessive radiation found in vegetables, tea, milk, seafood and water, despite official assurances that the levels were not dangerous.

The government foresaw the possibility of a meltdown, according to cabinet minutes, although it took officials more than a month to acknowledge it.

Cooling functions still in service are those run by batteries. They will last eight hours, a summary of the first emergency cabinet meeting, four hours after the quake, quoted an unidentified participant as saying.

If core temperatures in the reactors remain on the rise for more than eight hours, there is a possibility that meltdown may occur.

A Trade Ministry official who acted as a government spokesman was replaced after he mentioned the possibility of meltdown on March 12.

It was not until May that Tepco acknowledged that a meltdown of fuel rods appeared to have occurred, sparking criticism that the operator and officials were playing down the severity of the accident.

Tepco now believes that three of the six reactors at the plant, 240 km (150 miles) northeast of Tokyo, suffered fuel meltdowns.

(Additional reporting by Linda Sieg; Writing by Nick Macfie)