Police evacuated St. Rita of Cascia High School's students and staff after an alleged armed man ran onto school property, according to Chicago Police News Affairs.
It is unknown whether the suspect made it into the building, at 7740 S. Western Ave., where summer school is in session.
The armed suspect is wanted for another crime in the area, according to News Affairs.
Police dogs searched the school and found nothing. As of 1 p.m., police left the school.