A corrections officer was seriously injured during an altercation at Oak Park Heights prison on Wednesday, the state Department of Corrections (DOC) said.

The facility was placed on lockdown following the attack, said prison spokeswoman Sarah Fitzgerald.

The officer’s injuries are not life-threatening, authorities said. The incident is under investigation.

According to the DOC, the on-duty sergeant was attacked by an offender Wednesday morning. The officer fought back and was assisted by other correctional officers.

The offender is serving a life sentence for aiding and abetting second-degree murder.

Fitzgerald said new charges are expected to be filed against the offender.

Earlier this year, several staff members were injured during two fights in a span of a few days. The 10 staff members were seen at the hospital and released.

“This is a reminder of the difficult job our corrections officers do every day to keep Minnesotans and our prisons safe,” Fitzgerald said in a statement.

Oak Park Heights opened in 1982 and houses up to 473 offenders, most of whom are classified as “maximum custody or extreme risks to the public,” according to information on the state’s website.