Update: as of this morning, one of the inmates transported to the hospital has died, bringing the death toll to four.

Oklahoma State Correction Officials are investigating an incident that left three prisoners dead and five other inmates injured. The incident occured Saturday at a private correctional facility in Cushing.

Staff at the privately owned Cimarron Correctional Facility reportedly stopped an “disturbance” around 4:40 p.m., according to a statement released by Corrections Corporation of America, the facility’s parent company.

This is the second incident of this type at the facility this year. Earlier this year, 11 maximum security inmates were hospitalized after a brawl that involved nearly 300 inmates was put down by prison staff. The facility houses nearly 1,500 medium security prisoners and 200 maximum security inmates. Cimarron, like many privately operated facilities in Oklahoma is faced with near capacity population, while dealing with staff shortages.

Local officials are currently investigating the incident. No further details regarding the disturbance have been released including the cause, or the names of the dead and injured inmates. Reportedly the disturbance was confined to a single housing pod and lasted about 40 minutes.

The facility, located about 44 miles west of Tulsa, was put on lock-down as the staff worked to control the commotion.