ELOY, Ariz. — Twelve inmates and at least one guard at a private southern Arizona prison were injured Sunday during an apparent riot that took hours for authorities to contain, a prison spokesman and police said.

The violence began around 8:30 a.m. at Red Rock Correctional Facility in Eloy, Arizona, after “an inmate-on-inmate disturbance,” according to Jonathan Burns, a spokesman for the Nashville, Tennessee-based CoreCivic, which operates the prison.

But Eloy’s police department posted on its Facebook page about 2 p.m. that prisoners were “rioting” at Red Rock — more than four hours after the violence began. “At this time the situation is not contained and CCA special operations teams are working to secure the prison,” Eloy police said at the time.

“All inmates and staff are accounted for and the facility has been secured,” Burns said in a statement Sunday afternoon. “CoreCivic is cooperating fully with an investigation being conducted by its government partner at the Arizona Department of Corrections.”

Burns said 12 inmates were transported to outside medical facilities for treatment of non-life-threatening injuries and one CoreCivic staff member was treated and released from a hospital for minor injuries.

Eloy police said officers were on scene for a short time to maintain the outer perimeter of the prison and to support Eloy Fire Paramedics as they attended to injured people.

Arizona Department of Corrections staff and local law enforcement are reviewing and investigating the prison disturbance.