At least eight people — and as many as 10 — have died as a result of a shooting Friday morning at a high school in the southeastern Texas city of Santa Fe, Harris County Sheriff Ed Gonzalez said.

This is the third school shooting in eight days, and the 22nd since the beginning of the year in the United States.

A male suspect, believed to be a student, has been arrested in the shooting at Santa Fe High School, about 20 miles outside Galveston, Gonzalez said.

A second person — also believed to be a student — has been detained as well, Gonzalez said.

Most of the dead are students, the sheriff said.

Witnesses described students running from the school as they heard gunshots; they also described hearing an alarm at the school, though the sequence of events wasn’t immediately clear.

An armed person walked into an art class at the school and began firing what looked like a shotgun, a witness told CNN affiliate KTRK.

The witness told KTRK she saw a girl shot in the leg.

At least 12 people from the school are being treated at three hospitals, authorities said. Seven people are at Clear Lake Regional Medical in Webster, Texas; two patients are being treated at Mainland Medical Center in Texas City and three patients are at John Sealy University of Texas Medical Branch in Galveston.

At least one police officer was injured, Gonzalez said.