SACRAMENTO, CALIF. ? Inmates at the state prison in Calipatria remained locked in their cells Friday as authorities investigated a deadly riot that erupted in an exercise yard and spread to two buildings.

One inmate was killed during the uprising Thursday afternoon at the prison east of San Diego, and 25 inmates and 25 guards were injured.

Authorities said the fight began when a correctional officer was attacked by a member of the Southern Hispanic prison gang as he tried to search the inmate. About 20 other gang members piled on, slashing the guard five times in the head.

“In the buildings, the inmates were using broken broom handles and crutches and they were ramming the employees with laundry carts,” said Terry Thornton, a spokeswoman for the California Department of Corrections and Rehabilitation.

Inmate Richard Albert Zamora, 33, was shot in the abdomen by a semiautomatic rifle and killed during the fighting, authorities said. Zamora had been serving an 18-year sentence for vehicular manslaughter while intoxicated.

On Friday, more than 90 inmates were in segregation units, while other inmates were locked in their cells. Five inmates and 22 guards required hospital treatment.

The prison houses more than 4,000 inmates, more than 3,850 of them maximum security.