DENVER (AP) — Three teens were critically wounded in a shooting at a suburban Denver high school, including the suspected shooter, on Wednesday, authorities said.

The shooting was reported around 12:30 p.m. at Evergreen High School in Evergreen, about 30 miles west of Denver, Jefferson County Sheriff’s Office spokesperson Jacki Kelley said.

It is not clear what led up to the shooting or how the suspected shooter, believed to be a student at the school, was shot. None of the law enforcement officers who responded to the shooting is believed to have fired any shots, Kelley said.

The shooting happened on school grounds but it wasn’t immediately known whether it was inside the school building, she said.

All three teens taken to St. Anthony Hospital in Lakewood, Colorado, were shot, CEO Kevin Cullinan said

Over 100 police officers from around the Denver area rushed to the school to try to help, Kelley said. The sheriff’s office is the same agency that responded to the school shooting at the 1999 Columbine High School shooting that killed 14 people, including a woman who died earlier this year of complications from her injuries in the shooting.