Seven inmates were killed and 17 others were injured in an incident at Lee Correctional Institution in Bishopville, South Carolina, authorities said.
The fight started Sunday night at 7:15 p.m. ET and wasn't contained until 2:55 a.m. ET Monday morning, a prison spokesman added. It said that the incident played out over three housing units.
The Department of Corrections says the prison was secured just before 3 am Monday.
According to tweets from the Department of Corrections, all staff and responding law enforcement are safe and accounted for.
Additional details stating the cause of the fight have yet to be released. Aid was received from Florence County EMS, Kershaw County EMS, Darlington County EMS, Lexington County EMS and Hartsville Rescue.