A private prison in Arizona is on lockdown after a brawl broke out that involved as many as 150 minimum-security inmates and left a staff member and 12 prisoners with minor injuries.

The Arizona Department of Corrections said the fight broke out before 10 p.m. Wednesday but was contained within an hour.

A 20-member tactical unit from Arizona State Prison Complex-Tucson responded to help put down the disturbance.

The Marana Community Correctional Treatment Facility near Tucson houses 500 inmates and is owned and operated by Management and Training Corp., based in Centerville, Utah.

The cause of the fight is under investigation.