Five staff members at Oak Park Heights prison were injured during a fight involving prisoners Friday night, a Minnesota Department of Corrections official said Sunday.

The five went to the hospital and were released the same day, said Sarah Fitzgerald, the Department of Corrections spokeswoman.

Officials are sharing little else about the incident, which is still under investigation, Fitzgerald said.

Oak Park Heights in Stillwater is the state’s maximum-security facility. Opened in 1982, it houses up to 473 offenders, most of whom are “classified as maximum custody or extreme risks to the public,” according to the website.