TOKYO - Biscuits and vegetable juice for breakfast, no lunch and a packet of rice with canned fish or meat for supper. No showers, no beds and virtually never a change of clothes.

That's the grim lot of hundreds of workers toiling in perilous conditions to avert a catastrophic nuclear meltdown at Japan's earthquake-wrecked Fukushima power plant.

"This is similar to a war zone and things need to be addressed, including providing proper back-up for the workers who are under immense stress," said Hirotada Hirose, professor of disaster psychology at Tokyo Woman's Christian University.

"If this continues, productivity and morale will fall, and workers will become likely to make mistakes. We cannot afford that," Hirose said.

First dubbed the "Fukushima Fifty", the ranks of the unnamed and largely unknown corps of men risking their lives to prevent further disaster for their countrymen has risen to over 400. Feted by foreign media and on social networks as heroes, they have also won quieter admiration and sympathy from Japanese. But little was known until now of the dire living conditions that they faced in addition to the risks from radiation inside the buildings housing the stricken nuclear reactors.

The air around the plant is so contaminated by radiation that the men have to wear masks even when they are huddled inside the so-called safe room where they eat and sleep. They eat only packaged food, ramming it quickly into their mouths as soon as it is opened to avoid contact with radiation.

"I don't think the workers are getting enough nutrition from the food they are receiving," the Sankei Sports newspaper quoted Kazuma Yokota of the nuclear safety agency as saying at a news conference.

More than a dozen workers have been injured at the plant north of Tokyo, which was crippled by the March 11 earthquake and tsunami. Two were taken to hospital due to suspected radiation burns last week.

After a 7 am meeting, the workers from plant operator Tokyo Electric Power Co Inc and other firms such as Toshiba Corp head out to various sites within the complex before returning to the safe room around 5 pm. Early in the evening, they gather around to raise their spirits before wrapping themselves in blankets to sleep on the floor.

Top government spokesman Yukio Edano conceded more could have been done for the workers but told a news conference the priority had to be averting a massive disaster at the plant.

"We have been doing the best we can for the workers, but it hasn't necessarily been enough because we've had to put our priority on containing the accident."

Reuters