The embattled operator of Japan's Fukushima Daiichi nuclear plant has released workers' accounts of the desperate moments surrounding the huge earthquake and tsunami that triggered an atomic crisis.

At a hearing into the March disaster, a chief operator described how he realised disaster had hit when lights flickered and went out, including those on the control panels, according to an interim report released Friday by the Tokyo Electric Power Co. (TEPCO).

"I came to realise a tsunami had hit the site as one of the workers rushed into the room, shouting 'Sea water is gushing in!'", the unnamed chief operator was quoted as saying.

"I felt totally at a loss after losing power sources," he said. "Other workers appeared anxious. They argued, and one asked: 'Is there any reason for us to be here when there is nothing we can do to control (the reactors)?'"

"I bowed and begged them to stay."

The 9.0-magnitude earthquake and subsequent tsunami on March 11 paralysed electrical and cooling systems at the nuclear power plant, triggering the world's worst nuclear crisis since Chernobyl 25 years ago.

Friday's interim report was the first to detail testimonies from workers, who were hailed as heroes in the weeks following the accident as they took extreme health risks to try to prevent a worse nuclear disaster.

They described attempts to release pressure from a reactor container by manually opening a ventilation valve.

"We put on the full protection gear but couldn't possibly let young workers do the task, as we had to go into an area where the radiation levels were high," one worker recalled.

"When I got to the place to open the valve, I heard eerie, deep popping noise from the torus (a donut-shaped structure at the bottom of the reactor)," he said.

"When I put one of my feet on the torus to reach the valve, my black rubber boot melted and slipped (due to the heat)."

The operators also spoke of dismal working conditions as they battled to stabilise the crippled plant.

"We experienced big aftershocks, and many times we had to run up a hill in desperation (fearing a tsunami) with the full-face mask still on," one worker said.

Another worker spoke of the race to lay power cables and bring back the supply of electricity, saying: "We finished the work (in one section) in several hours, although it usually requires one month or two."

"It was an operation we had to do in puddles, fearing electrification," the worker said.

Explosions and fires at the plant unleashed dangerous levels of radiation, forcing TEPCO to pull out hundreds of workers, leaving just a few dozen behind.

Those workers earned the nickname "the Fukushima Fifty", but that number eventually swelled again by thousands, including technicians sent from partners such as Toshiba and Hitachi.

They were tasked with keeping cooling water flowing into the six reactors at the plant, three of which eventually overheated and experienced meltdowns.

Despite a series of setbacks in the past nine months, the Japanese government and TEPCO say they remain on track to declare a cold shutdown later this month, about a month earlier than initially planned.

The atomic accident has not directly claimed any lives but has left tens of thousands of people displaced and rendered whole towns uninhabitable because of radiation, possibly for decades. The quake-tsunami killed about 20,000 people.

In a recent interview with AFP, Goshi Hosono, state minister in charge of nuclear accident settlement and prevention, hailed the plant workers for their battle to tame the crippled reactors.

"It was the emergency workers at the plant who have contributed to it the most," he said. "We are finally seeing the goal of cold shutdown in sight. The workers' efforts must be highly applauded."

But Hosono, when he visited the plant last month, also cautioned that 30 years' work remained to be done to dismantle the machinery.

Last month, then Fukushima Daiichi plant chief Masao Yoshida told state broadcaster NHK: "In the first week immediately after the accident I thought a few times 'I'm going to die.'"

Referring to a hydrogen explosion that tore apart the buildings around rectors 1 and 3, he said: "I thought it was all over."