A corrections officer at Oak Park Heights state prison died Monday after rushing to help another officer who was being assaulted by an inmate.

Joseph Parise, 37, was one of several officers who responded at noon to break up the assault, the latest such violent incident at Minnesota prisons this year. He then went back to his post, where he suffered a "medical emergency," according to the Minnesota Department of Corrections.

Parise was taken to Regions Hospital in St. Paul, where he died, according to a statement from department spokeswoman Sarah Fitzgerald.

The cause of death was still unknown, she said. The prison remained under lockdown late Monday afternoon and an investigation was underway, she said.

"We are deeply saddened by today's events," she said. We offer our heartfelt condolences to Officer Parise's family, friends and all of his fellow officers."

Two employees hurt during the altercation were evaluated at the hospital and released.

Officials with AFSCME Council 5, the union that represents 2,000 corrections officers in Minnesota, said in a statement that Parise had worked for the Department of Corrections for four years.

"We offer our deepest respects to our fallen brother for his courage and his service," the union said. It said Parise and a case worker rushed to help when the inmate repeatedly punched a corrections officer in the face at noon Monday.

Corrections officers have been calling on the state to hire more guards for months, following several violent attacks against officers this year.

Joseph Gomm, a 45-year-old corrections officer from Blaine, was killed in July at Stillwater prison, and an inmate is accused of the crime. Gomm was the first Minnesota corrections officer to be killed in the line of duty.

A month before his death, a corrections officer at Oak Park Heights was slashed repeatedly with a razor in the face, hands and scalp.

In March, 10 officers were injured in the same week after two fights broke out among inmates. All 10 were treated and released from a hospital that same day.

Guy Wicklander, a retired Stillwater corrections officer, said the attacks were putting more and more pressure on officers.

"Just in a normal situation it's a stressful job," said Wicklander, who was nearly killed during a 1999 inmate attack at Oak Park Heights. "But especially right now."

Oak Park Heights corrections officers have set up a GoFundMe page to raise money for Parise's family.