Six workers at Japan's Fukushima nuclear plant have been doused in radioactive water, its operator says.
The incident happened after a worker removed a pipe connected to a water treatment system at the plant, Tokyo Electric Power Company (Tepco) said.
A senior official from Japan's nuclear watchdog said he did not believe the workers had received a "seriously troubling" dosage of radiation.
Fukushima has been hit by a series of toxic water leaks in recent months.
The plant was badly damaged by the earthquake and tsunami of March 2011. Cooling systems for reactors were knocked out, causing meltdowns at three of them.
Water is being pumped in to cool the reactors. However, this creates large amounts of contaminated water that must be stored securely.
Some of the water has leaked from the tanks, pipes and damaged structures, leading to concerns contaminated water is mixing with groundwater that is flowing into the sea.
The detached pipe was connected to a desalination system, Tepco said, which was being used to treat toxic water before storage in tanks.
Tepco said it was measuring the radiation that the workers, who were wearing protective gear, were exposed to.
"It is serious in that it was another problem caused by carelessness, but I do not believe it is a seriously troubling dosage," Shunichi Tanaka, chairman of Japan's Nuclear Regulation Authority, was quoted as saying by Reuters news agency.