RICHMOND, Calif. (AP) _ An explosion and fire rocked a plastics factory Thursday, killing one worker and injuring at least four others.

Because of smoke from the blaze, people living nearby were told to stay indoors and keep their windows closed, and classes were canceled at seven schools.

The cause of the 2 a.m. blast at MBA Polymers Inc., a research and commercial recycling operation, was not immediately known.

The injured were treated for smoke inhalation, the Fire Department said.