TOKYO >> Six more workers at Japan’s tsunami-damaged nuclear power plant may have exceeded the radiation exposure limit, bringing the total to eight, the government said today.

The health and labor ministry released the preliminary results of tests on how much radiation they had been exposed to as they worked at the Fukushima Dai-ichi plant. Three men are control room operators and the five others worked to restore power that was knocked out by the earthquake and tsunami March 11.

Operator Tokyo Electric Power Co. said none of them was showing immediate health problems but would require long-term monitoring as they have an increased risk of cancer. All eight have been transferred to desk jobs.

“We find it extremely regrettable,” said Tadashi Mori, a health ministry official in charge of occupational health, referring to the six likely additions. Mori said the ministry plans to take “appropriate steps” over TEPCO’s violation when the results are confirmed.

The government soon after the disaster raised the radiation limit for men to 250 millisieverts from the standard 100 millisieverts so workers could tackle the emergency.

The health ministry also said Monday that at least 90 others have exceeded the earlier limit of 100 millisieverts, including several who are nearing the higher limit.

On Friday, the Nuclear and Industrial Safety Agency said that the first two workers who reached the government’s limit had been exposed to more that double that amount. It reprimanded TEPCO and demanded an investigative report within a week. The health ministry separately submitted a written warning over the two workers’ exposures and is likely to do the same for the six additional workers if their cases are confirmed.

The two control room operators were exposed to more than 600 milisieverts — about 100 CT scans — mostly by inhaling radioactive particles, NISA spokesman Hidehiko Nishiyama said.

The newly confirmed six workers may have exposures from about 265 millisieverts to 498 millisieverts, mostly while working at the plant March 12 when a hydrogen explosion heavily damaged the Unit 1 reactor building, TEPCO spokesman Junichi Matsumoto told a news conference.

TEPCO already has admitted that workers in the earliest, most chaotic, and most dangerous moments of the crisis did not wear masks, possibly other protective gear as well, and lacked dosimeters to monitor their radiation exposures in real time. TEPCO has been warned for failing to observe a legal requirement to provide a dosimeter each for those entering controlled areas.

Workers have been fighting to get the plant under control since the quake and tsunami knocked out its power and cooling systems, largely melting three reactor cores. Explosions, especially in the immediate days after the disaster, scattered radioactive particles and debris around the plant, making their working environment highly dangerous.

“The workers had received safety instructions, but I believe that probably slipped their mind in the crisis,” Matsumoto said.

Matsumoto said the operator now removes workers from the plant work when their exposures exceed 150 millisieverts, without giving further details. It wasn’t immediately clear if more workers, beyond the eight exposed to more than the government-set limit, have been reassigned to other jobs.

The revelation about the workers’ high exposures have boosted concerns about health risks at the plant.

About half of the nearly 4,000 people who had worked at the plant during March have been checked for internal exposures so far, with further examination pending. Mori said there could be more workers exceeding the limit.

A massive single whole-body exposure of 500 millisieverts could decrease lymphocyte cells in some people, which would compromise their immune systems. Radiation sickness, which has the signature symptoms of nausea and hair loss, can occur from an acute dose of 1,000 millisieverts.