A riot this morning at one of the two state prisons in Folsom involved about 150 inmates and multiple weapons, officials from the California Department of Corrections and Rehabilitation said.
At least two inmates at California State Prison, Sacramento, were stabbed multiple times and were taken to an outside hospital for treatment, following the riot at about 10 a.m.
The severity of their wounds was not immediately available.
The riot took place in the exercise yard of B-Facility, a maximum-security unit in the prison, said LeVance Quinn, a spokesman for the CDCR.
Various groups were involved, but no specifics were available, Quinn said.
Prison staff used rubber bullets and pepper spray as well as one warning shot fired using a lethal round.
Injuries are being assessed, but most inmates sustained only minor injuries, officials said.
The entire prison is on modified program, or lockdown, while the riot is under investigation.
The lockdown will continue in B-Facility until further notice.
California State Prison, Sacramento, is in Folsom, but is distinct from Folsom State Prison.
It houses about 3,000 inmates, primarily in maximum security for longer sentences.