By Jason Hanna, Dakin Andone and Keith Allen, CNN

(CNN) -- Someone opened fire at a high school in the southeastern Texas city of Santa Fe on Friday morning, officials said, leaving more than one person injured and students running from the school.

A suspect in the shooting at Santa Fe High School has been arrested, assistant principal Cris Richardson told reporters near the school.

An armed person walked into an art class at Santa Fe High 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. Witnesses also described hearing an alarm at the school, though the sequence of events wasn't immediately clear.

Patients from the school are being taken to a hospital in the nearby city of Galveston, hospital spokesman Raul Reyes said. He did not say how many or give details about the injuries.

The school district, in a statement, also said more than one person was injured.

Aerial video from the scene showed several police officers outside the school. Some were searching students and their backpacks.

Angelica Martinez, a 14-year-old student, told CNN she and her schoolmates were being evacuated at one point "like it's a fire drill."

"We were all standing (outside), but not even five minutes later, we started hearing gunshots," she said. "And then everybody starts running, but like the teachers are telling us to stay put, but we're all just running away."

"I didn't see anybody shooting, but like (the gunshots) were kind of spaced," Angelica said, adding she heard about four shots.

The witness who spoke to KTRK also said she heard an alarm. She didn't specify if that was before or after the gunfire she described in the art class.

She said she couldn't describe the shooter.

"I didn't look. I just ran," she said.

The entire school district is on lockdown, district officials said.

Santa Fe is a city of about 13,000 people roughly 20 miles northwest of Galveston and 30 miles southeast of Houston.

The high school has about 1,400 students, according to GreatSchools.org.

Developing story - more to come