Arizona State Prison Tucson
A 400 inmate fight broke out at Arizona State Prison in Tucson on Sunday. Arizona Department of Corrections

A fight involving 400 inmates has caused Arizona State Prison, located in Tucson, to shut down. The enormous melee erupted in a minimum-security location within the prison. Of those involved, 19 were injured including 17 inmates and two prison gutards.

The fight occurred on Sunday morning and was quickly broken up, reports The Associated Press. The guards were treated for minor injuries while the 17 inmates were taken to local hospitals.

Arizona State Prison is separated into eight different units. The massive melee occurred at the Whetstone Unit, which houses approximately 1,250 inmates, notes AP. After the fight, prison officials canceled all visitations scheduled for Sunday, and the prison is currently on lockdown. The fight involved 100 African-American inmates and 300 Caucasian and Mexican-American inmates, according to ABC15.

Prison officials do not know what led to the fight, but many speculate that racial tensions were at the heart of it. Daily Mail describes the melee as a “race riot,” citing previous investigations into racial profiling by Maricopa County Sheriff Joe Arpaio from 2012. In September 2012, a fight involving 200 inmates occurred at the Santa Rita Unit of the Arizona State Prison, reports The Arizona Republic.

Earlier this year, two other small-scale inmate fights led to prison lockdowns in Annapolis, Md., and Seattle. On Feb. 8, in Jessup Correctional Institution, a maximum-security prison, an inmate got into a confrontation with an officer that prompted several other inmates to attack nearby officers, according to an earlier AP report. On Feb. 18 at Airway Heights Corrections Center, in Seattle, a 16 inmate fight led to a prison-wide lockdown. Three prison guards were treated for minor injuries sustained when they tried to break up the fight and an inmate was taken to a local hospital for treatment.