Government officials in Japan say at least eight workers trying to bring the crippled Fukushima nuclear power plant under control have been exposed to excessive radiation.
Three of the six reactors at the Fukushima melted down after the earthquake and tsunami on 11 March knocked out power to the plant.
It was the world's worst nuclear accident since Chernobyl in Ukraine in 1986.
The Tokyo Electric Power Company previously said two workers had been exposed to more radiation than is allowed.
Officials says the exposure of the additional six workers was discovered after almost 2400 workers underwent testing.
Tepco said none of those affected were showing immediate health problems, but they would require long-term monitoring.
Japan's Nuclear & Industrial Safety Agency said the development was ''extremely regrettable''.