An inmate at Rush City prison attacked a corrections officer Wednesday morning, prompting a lockdown of the high-security unit where the assault took place.

The officer was at the officers' desk when she was punched in the face. She defended herself until colleagues arrived to restrain the inmate, said Department of Corrections (DOC) spokeswoman Sarah Fitzgerald. The assault occurred in a housing unit about 7 a.m.

The officer was treated at an area hospital. The unidentified inmate was immediately placed in restrictive housing, Fitzgerald said.

The attack comes amid escalating concerns about the safety of on-duty corrections officers.

Last week, the DOC delayed reopening an industrial building on the sprawling Stillwater prison campus after 30 employees refused orders to return to work without increased staffing and security.

AFSCME Council 5, the labor union that represents 2,000 corrections officers in Minnesota, said that its members remain shaken from the loss of veteran Stillwater corrections officer Joseph Gomm, who was beaten to death in July by a violent offender.

A yearly breakdown of discipline convictions obtained by the Star Tribune chronicles a 66 percent spike in overall assaults on prison personnel this year throughout the state.

As of June 30, the DOC reported 17 assaults on Rush City staff, up from 11 assaults last year.

In a statement, Fitzgerald said Wednesday’s assault will be investigated and the inmate will be held accountable.

“Our highest priority at the Minnesota Department of Corrections is protecting the safety of our officers and all individuals in our facilities,” Fitzgerald said. “An assault on a member of our staff is taken extremely seriously.”

Rush City prison is the DOC’s newest facility and houses 1,020 male inmates. Nearly one-third of the population is serving an extended sentence for a murder conviction.