Updated

One inmate was seriously injured and a fire was started in a Nebraska state prison known to have a history of riots, after 16 cells unexpectedly opened Friday, officials say.

The Nebraska Department of Correctional Services said that 16 single-person cells at the Tecumseh State Correctional Institution “were opened in error” shortly before 10 a.m.

Officials said that inmates refused to get back in their cells, but that no staff members were in the gallery at the time the doors opened. They unsuccessfully attempted to use chemical agents to force the inmates back in their cells.

“The corrections emergency response team (CERT) was activated and prepared to enter the gallery; however, the incident resolved with the inmates complying with staff directives,” the statement read.

The Tecumseh Volunteer Fire Department also responded to the scene because a fire started in one of the cells. The cause of the fire remains unclear.

One inmate was attacked by “one or more others” and was seriously injured. No staff members were injured but one person was treated for possible smoke exposure.

Nebraska State Patrol is investigating what led the doors, which are operated by a computerized system, to open.

All the inmates were accounted for and the facility is under “modified operations” until further notice.

The prison has a troubled history. Last year, two inmates were killed and others were injured in a riot that included a prison courtyard fire. That riot happened in the same housing unit where two other inmates were killed during a May 2015 uprising that caused about $2 million in damage.

The riots and other incidents, such as attacks on prison staff, have led lawmakers and other officials to scrutinize Nebraska's prison system. The Legislature this year passed a package of bills designed to address the state's chronically overcrowded prison system and understaffing. That included a July 1, 2020, deadline to lower overcrowding from 160 percent to 140 percent of capacity.

The Associated Press contributed to this report.