PETERBOROUGH, N.H. (AP) — An explosion at a New Hampshire ball bearings plant has injured at least 13 people, but a company spokeswoman says none of the injuries appears to be life-threatening.

Spokeswoman Kathy Gerrity says it's unclear what caused the explosion Monday afternoon at New Hampshire Ball Bearings Inc. in Peterborough.

Monadnock Community Hospital spokeswoman Laura Gingras (JIN'-grahs) says 13 people were treated there. She says two were then flown to other hospitals and six were released by Monday evening.

The southwest New Hampshire plant employs 700 people. Gerrity says she's unsure how many people were inside when the explosion happened Monday afternoon but there are usually about 450 working around that time.

New Hampshire Ball Bearings' corporate headquarters are in Chatsworth, Calif. It's a division of Japanese company Minebea.