BAYPORT, Minn. (AP) — A corrections officer died Wednesday after authorities say he was assaulted by an inmate at Minnesota's flagship Stillwater state prison. The death prompted a lockdown at Minnesota's prison system.

Officer Joseph Gomm was attacked by an offender at the state's flagship prison at 1:30 p.m. Wednesday, the Minnesota Department of Corrections said. Gomm was taken to Regions Hospital in St. Paul but was pronounced dead at the hospital, the department said.

"The corrections family is reeling from this incident," state Corrections Commissioner Tom Roy told reporters. "We are not accustomed to losing staff."

Roy declined to identify the inmate, who was serving time for homicide. He said the inmate was believed to be "the lone perpetrator."

The attack happened in the prison's industry building, which houses a welding shop and carpentry programs. Authorities did not give details about the assault. The Minnesota Bureau of Criminal Apprehension has arrived at the prison to investigate, Roy said.

Roy called Gomm "a fine man doing honorable work" who had just celebrated his 16th year as a corrections officer the previous day.

In a statement, Gov. Mark Dayton said he was "appalled" by Gomm's killing, and offered his sympathies to the officer's family, friends and fellow corrections officers.

Mark Groves, president of the Minnesota Corrections Association, said the union was "deeply saddened" by Gomm's death but referred questions to the Department of Corrections.

Roy, the corrections commissioner, said the Stillwater prison, and others in the system, are on lockdown in "an abundance of caution" while authorities assess whether the attack was an isolated incident. He said he did not expect the lockdown to continue.

A corrections officer was assaulted earlier this year at the prison. Stillwater has two levels of security, minimum and "close." The latter ranks just below maximum security. Roy said the prison had 1,616 prisoners, about one-third of them serving homicide sentences.

In March, assaults by inmates at the Minnesota Correctional Facility-Oak Park Heights sent 10 employees to the hospital. Last month, the maximum security prison was placed on lockdown after an inmate attacked a corrections officer, causing serious injuries.