St. Louis police say three people are dead, including the shooter, after a shooting at a high school Monday morning.

Police Commissioner Michael Sack said the three dead included a woman, a teenage girl and the shooter, described as a man about 20 years old.

The shooting just after 9 a.m. at Central Visual and Performing Arts High School forced students to barricade doors and huddle in classroom corners, jump from windows and run out of the building to seek safety.

Sack said security officials initially became alarmed when the shooter tried to get into the locked school building. He declined to say how the man got inside, armed with what he described as a long gun.

Officers “ran to that gunfire, located that shooter and engaged that shooter in an exchange of gunfire,” killing him, Sack said.

Sack declined to name the victims and did not say if the woman who was killed was a teacher.

Six other injured people were hospitalized. Sack said some suffered gunshot wounds, while others were struck by shrapnel. He did not provide any information on their conditions.