A boiler exploded at Sumitomo Metal Industries Ltd. (5405)'s largest steel factory, north of Tokyo, injuring one worker.

The explosion at Kashima steelworks in Ibaraki prefecture occurred at 1:46 p.m. today, Reiko Ishihara, a spokeswoman for the Japanese company, said today by phone. The cause of the accident is being investigated, she said.

The boiler is not used often and the explosion won't affect operations at the plant, Ishihara said. Kashima produces more than half of the company's crude steel.

Ibaraki police confirmed a Kyodo news report earlier today on the explosion.