One person was killed and at least four others were injured in a shooting at Saugus High School in Santa Clarita on Thursday morning, authorities said.

The shooting was reported at the campus at 21900 Centurion Way about 7:40 a.m., prompting a massive law enforcement response. Paramedics swarmed the campus, treating the wounded while authorities combed nearby neighborhoods searching for a 15-year-old boy suspected in the shooting. Agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Los Angeles County Sheriff’s Department SWAT team also assisted with the search.

After roughly an hour, authorities said that the suspect, who is believed to be a student at the school, had been apprehended. The teen, who was not immediately identified, is being treated at a hospital and is in unknown condition, Sheriff Alex Villanueva said.

Four people from the school were transported to Henry Mayo Newhall Hospital for treatment. One patient, a female, died there. Two male patients are in critical condition and one male is in good condition, according to Patrick Moody, a spokesman for the hospital. Their specific injuries and ages were not immediately provided.

The scene at the high school was chaotic, with teenagers walking in a line behind armed law enforcement officials with their arms raised in the air immediately after the shooting. Many of the injured were being treated in a grassy area on the campus before being placed on gurneys and transported to ambulances in the school’s parking lot. At least one person was found wounded in the school’s choir room, authorities said.

Some students remained locked in classrooms for more than an hour as authorities searched for the shooter. Eventually, they were led off the campus by deputies. Some were in tears. As they walked, one student asked aloud a question on the minds of many others across the state: “What kind of a world is this?”

All schools in the William S. Hart Union High School District were locked down as authorities searched for the shooter. Authorities had been centering much of their focus on the brushy area behind the high school adjacent to a creek where authorities thought the shooter might have been hiding. Law enforcement officials were also searching the backyards of homes along Sycamore Creek Drive. It is not clear where he was eventually located.

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Parents are being directed to Central Park on Bouquet Canyon Road to be reunited with their children.

Denzel Abesamis, a senior at Saugus, was driving to school and about to turn onto campus when he saw classmates running out and turned around. He called a friend who he knew was on campus. She told him there was a shooter and she was hiding in a classroom with five other students.

During his freshman year they also had a lockdown after reports of a threat.

“I’ve always been worried about something like this would happen since it was my actual school,” he said. “Saugus has emphasized the importance of making sure to always be cautious of anything that may happen like an active shooter.”

Michael Harrison, 26, said he first became aware of the shooting when his younger sister, a 17-year-old senior, texted him: “there is a shooter, call 911.”

“I can’t even describe it, man,” Harrison said with a panicked laugh. “Imagine getting that text.”

Harrison and Kimberly Simpson, 30, were standing next to one another across the street from Saugus High’s main entrance, where dozens of emergency vehicles and sheriff’s deputies in tactical gear had flooded the street, some parking in private driveways. One deputy could be heard telling a parent that law enforcement was conducting a “systematic search” to clear all the classrooms.

Simpson’s 15-year-old daughter, a junior, was in class Thursday morning when a teacher ordered students to do what they had drilled for, referring to lockdown procedures after a shooting.

“She’s freaked out. She’s scared,” Simpson said. “I don’t know if she’s going to want to go back.”

Simpson’s 14-year-old son, a freshman, was also on his way to school but was running late, so she pulled him back inside his home after reports of gunfire surfaced. Another one of her children, a 10-year-old boy, was on lockdown at a neighboring elementary school.

The shooting came two months after six students at the high school were detained on felony criminal charges after authorities were alerted to threats the teenagers had made online. A Hart Union staff member discovered the social media posts “regarding committing acts of school violence” and alerted authorities, according to the Sheriff’s Department.

Detectives quickly determined who had made the posts, according to the agency. It’s unclear whether those threats were connected to Thursday’s shooting.

Former U.S. Rep. Katie Hill stood in her backyard in Saugus as helicopters circled overheard searching for the gunman. Hill graduated from Saugus High School in 2004, when active shooter drills were never discussed. Thursday morning, her father sent her a text alerting her to the news.

“I’m absolutely horrified that it’s happening at my school,” she said. “Last heard the shooter was on the move towards the elementary school I went to.”

The community is a close-knit one. Hill said that several of her staffers are graduates of the high school, and currently know parents with students at the school.

“This is what we’ve all been afraid of,” she said.