Oregon officials say guards at the state penitentiary fired warning shots and used chemical spray to break up multiple fights involving about 50 inmates in the prison yard.
Corrections Department spokeswoman Jeanine Hohn said two staffers and one inmate suffered minor injuries in the Monday afternoon fights at the facility in Salem.
She says many inmates were taken to disciplinary segregation. Inmates who were not involved were being returned to their housing units.
The prison has been placed on modified lockdown, with all activities and visits canceled.
Oregon State Police have been notified and the fights are under investigation.