Two workers at Japan's crippled nuclear power plant may have exceeded the government's radiation exposure limit, the plant operator said, adding to concerns about health risks for those fighting the world's worst nuclear disaster in 25 years.

If confirmed, it would mark the first case of excess radiation exposure among the hundreds of emergency workers who have struggled to bring Tokyo Electric Power Co's (TEPCO) Fukushima Daiichi plant under control after it was wrecked by a massive earthquake and tsunami in March.

Both the government and the utility, TEPCO, have come under fire for not disclosing enough information about radiation doses and the risks. Some experts question whether workers have been fully informed of the potential dangers. "The problem is that too much policy has been focused on protecting TEPCO and not enough on the public," said Kiyoshi Kurakawa, a medical doctor who served as a science adviser to the government from 2006 to 2008.

Measurements of external exposure and radioactive iodine in their thyroid glands suggested that the two male workers, one in his 30s and the other in his 40s, had surpassed the maximum set by the government of 250 millisieverts over the life of the control and clean-up project.

Exposure to 250 millisieverts of radiation is equivalent to more than 400 stomach X-rays. That is below the level for acute radiation sickness. Experts are divided about the long-term health effect but agree higher levels of exposure correspond to higher risk of cancers.

The government relaxed its upper limit for exposure for the Fukushima disaster, allowing 250 millisieverts for male emergency workers compared with the conventional maximum of 100 millisieverts for nuclear-related emergencies.

A new poll showed on Monday that more than 80 percent of Japanese voters do not trust government information about the country's nuclear crisis.

The poll conducted by Fuji Television Network also found that nearly 85 percent of respondents said the utility that operates the stricken Fukushima Daiichi nuclear plant is dealing with the crisis poorly.

Eighty-one percent of respondents to the survey said they did not trust government information about the crisis, Fuji TV said. Seventy-eight percent said Prime Minister Naoto Kan lacked leadership in handling the disasters.

Kan is facing calls for his resignation even within his own ruling party. Opposition parties are expected to submit a no-confidence motion against him as early as Thursday.

Kan is likely to survive the motion because his Democratic Party of Japan controls the powerful lower house of parliament. However, some ruling party lawmakers may support the motion to pressure Kan to quit, local media say.

The national poll of eligible voters was conducted by telephone on May 28 to 29 and had 1,000 responses.