(CNN) -- [Breaking news update, published at 1:15 p.m. ET]

A female patient injured in Thursday's shooting at Saugus High School in Santa Clarita has died, a Henry Mayo Newhall Hospital spokesman said.

[Earlier version]

Someone opened fire at a high school in the Southern California city of Santa Clarita shortly before classes began Thursday morning, officials said, shooting and injuring several people and sending some students streaming out of the building as others hid.

A suspect in the shooting at Saugus High School is in custody and is being treated at a hospital, Los Angeles County Sheriff Alex Villanueva said on Twitter.

Details about how the suspect was captured weren't immediately available.

Authorities had been looking for a suspect described as an Asian male in black clothing, the sheriff's department said on Twitter. The suspect is believed to be a student at the school, Villanueva told CNN affiliate KABC.

Six patients -- three in critical condition -- have been taken to hospitals, officials at the facilities said. At least five were shot, a sheriff's department official said.

Emergency workers took at least three people out of the school on gurneys, and large groups of people walked out single-file with armed escorts, aerial footage from CNN affiliates shows.

The shooting happened about 20 minutes before the start of school, according to Hannah de Caussin, whose daughter attends Saugus.

Some students fled the building immediately, and others took cover inside rooms, another student told CNN affiliate KTLA.

"It was one and then four quick ones, so bang, and then bang, bang, bang, bang," the student, a girl, told CNN affiliate KTLA, after leaving the building.

Students are trained to take cover in classrooms, but she and some others ran out because they thought the shooter was near where they would have hidden, she said.

"We ran through the fence, luckily it was open, and we got as far away from campus as we could," she said.

"We were texting all our friends and making sure they were safe. They said they were hiding and they were scared. It scared us because they're our friends and we didn't want anything bad to happen to them."

All schools in Santa Clarita's William S. Hart school district were temporarily locked down as a precaution, but the restrictions were lifted at all but Saugus and Arroyo Seco Junior High by mid-morning, the district said.

Saugus High School, about 30 miles northwest of Los Angeles, has about 2,400 students, according to the district.

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