Patrick Henry High School in north Minneapolis was searched room by room, top to bottom, and armed police escorted groups of students out of the building over three hours Tuesday after someone believed to have a gun ran inside.
Parents waited anxiously until they made contact with their children.
A "code yellow" was called about 3:30 p.m., about 20 minutes after the school day ended, quickly followed by "code red," meaning students and staff members were ordered to lock classroom doors, shut off lights and pull curtains.
Hundreds of students, teachers and coaches were still scattered throughout the building for after-school activities and meetings.
Jania Kloeppel, 16, said she was in the auditorium when the alarm came over the intercom. She and the students with her hid in a prop room until police reached them.
"It's unnerving, but at the same time it's what's been going on in this country," she said. "In the back of my head I kind of knew something like this was going to end up happening, but I didn't think I was going to get caught in it."
Police said the male fled to the school and entered through a side door after trying to get on a Metro Transit bus. He left the school minutes later, police said in a news release Tuesday night.
Police spokesman John Elder said no shots were fired, no one was injured and no arrests were made.