One inmate was killed and five others were taken to an outside hospital to be treated for stab wounds after a riot Wednesday at a Northern California state prison.

The fight involving about 100 maximum-security inmates began when one inmate attacked another, "and then everyone else joined in," said Department of Corrections and Rehabilitation spokeswoman Dana Simas. The riot at California State Prison, Sacramento, involved members of multiple prison gangs, she said.

Correctional officers used pepper spray and fired three warning shots to stop the fight, which began shortly before 1 p.m. in an exercise yard. Despite the shots fired, Simas said there is no doubt the inmate was killed by a fellow inmate.

The victim's identity is being withheld until relatives are notified.

The five hospitalized inmates all suffered stab wounds, and numerous inmate-made weapons were recovered, she said. Other inmates were treated at the prison for their injuries.

No employees were hurt.

The prison commonly called New Folsom houses more than 2,300 maximum-security inmates in Folsom, about 25 miles east of the state capital.

Prisoners remained locked in their cells as officers investigate the disturbance.