CALIPATRIA  (AP) — Seven inmates were injured as violence broke out among some 200 inmates at a state prison in southwestern California.

A statement from Calipatria State Prison in Imperial County says the brawl broke out in a yard Tuesday.

Guards fired warning shots, pepper-spray rounds and rubber bullets, quelling the melee after about eight minutes.

Seven inmates were injured, none seriously. Six of them were taken to a hospital and returned to the prison. Most of the injuries were from the fighting, but one inmate needed stitches from a rubber bullet round.

Inmates are under lockdown while the cause is investigated. No staffers were injured.

Calipatria, a prison near the Salton Sea about 70 miles northeast of San Diego, houses about 3,800 men. Nearly half are serving life sentences.