The Kansas Department of Corrections has moved 100 inmates out of Norton Correctional Facility after a late-night disturbance that included a fire, smashed windows and two officers’ injuries, a spokesman said.

KDOC spokesman Samir Arif said Wednesday 50 inmates were transferred to Lansing Correctional Facility and another 50 were being scattered between other correctional facilities. He said the 100 inmates were initially identified as instigators in the uprising that started around 9:30 Wednesday night. Arif said the department had not yet proven those inmates started the disturbance and that an investigation into the event was underway at the prison that houses primarily medium-and minimum-security inmates.

Arif said the uprising started when inmates lit a mattress on fire and a dormitory was evacuated leaving 250 inmates in the prison yard in the dark. He said some broke into a supply closet and got shovels and rakes and broke windows, but the department did not yet know exactly who caused the problem and why.

“It’s difficult to tell exactly who was doing what and for what reason,” Arif said.

Two staff members were injured but did not require medical attention during the incident that started around 9:30 p.m. Tuesday night and ended just after midnight, according to KDOC. The Kansas Organization of State Employees, which represents corrections officers, called the disturbance a “huge riot” in a tweet Tuesday evening.

The disturbance was the latest in a period of prison unrest that also sparked a riot at El Dorado Correctional Facility in late June. Robert Choromanski, executive director for KOSE, said he thought the unrest had stemmed from transfers of inmates between correctional facilities that have been plagued by staffing shortages.

“That virus kind of spread,” Choromanski said.

Inmates were moved earlier this year from Lansing Correctional Facility. The number of inmates housed at El Dorado Correctional Facility also ticked down after a June 29 uprising. On Tuesday, Norton housed 856 inmates at its main unit and another 128 at is satellite unit to the east in Stockton.

Arif said few inmates had been moved from El Dorado to Norton and that the department was still investigating culpability. He said that process would likely take at least one week.

The Associated Press Contributed to this report.