SANTA CLARITA, Calif. - A 16-year-old student pulled a gun from his backpack and opened fire on classmates at a high school north of Los Angeles on Thursday morning, fatally wounding two teens and striking three others before turning the gun on himself, police said.

The shooter, whose attack unfolded at Saugus High School in Santa Clarita, survived his self-inflicted gunshot wound and was in grave condition at a hospital, authorities said. The suspect carried out the shooting on his 16th birthday, police said.

Someone called 911 to report the shooting at 7:38 a.m., according to authorities. When deputies arrived two minutes later, they found six students with gunshot wounds in the quad, a popular outdoor gathering spot with trees and picnic table. They later learned the shooter, who was dressed in black, was among them. They also recovered a .45-caliber semiautomatic handgun at the scene.

Television footage showed a familiar scene: a campus swarmed with ambulances and police cars, students evacuating school buildings while wounded classmates were wheeled out on gurneys, and worried parents clustered around the school's perimeter.

The shooting is at least the seventh to take place on U.S. school grounds since the start of the academic year, according to a Washington Post analysis, and the first fatal shooting on a campus since students arrived back at school. More than 233,000 schoolchildren have been exposed to gun violence at their own schools since the shooting at Columbine High in 1999.

"We need to say 'no more.' This is a tragic event that happens too frequently," said Capt. Robert Lewis of the Santa Clarita Valley Sheriff's Station. "When are we going to come together as a community . . . to say 'no more'?"

Four people were taken to Henry Mayo Newhall Hospital in Valencia, California, including the 14-year-old boy and 16-year-old girl who died. A third person was in critical condition and a fourth was treated and released.

Two other girls were taken to Providence Holy Cross Medical Center and were talking when they arrived, Patricia Aidem, a hospital spokeswoman, said. One girl was listed in good condition and the other in fair condition.

A seventh person was treated for injuries that were not critical, officials said.

Authorities would not say where the shooter was being treated.

The shooter was identified through witness statements and school security footage, which captured the attack, law enforcement officials said. The suspect's mother and girlfriend were interviewed by law enforcement.

At an early evening news conference, authorities said just 16 seconds passed from the time the shooter drew his gun and when he shot himself. They said that the shooting was contained to the quad and that they had no information about a connection between the shooter and his victims.

"At this point we have no indication of any motivation or ideology," said Paul Delacourt of the FBI's Los Angeles Field Office.

Santa Clarita is a city of about 210,000 nestled in a large brush-covered valley about 30 miles northeast of Los Angeles. Saugus High, on a campus lined with palm trees, has about 2,400 students, according to federal data. Earlier this year, a half-dozen students from Santa Clarita were detained on charges stemming from violent threats posted online, the Los Angeles Times reported.

The scene outside Saugus High was quiet except for the thwack of helicopters overhead and the rumbling of idling firetrucks and police cars. The area around campus had been blocked off with police tape.

On a quiet street nestled beneath a wooded hill three miles away, police barricaded the road near the house where they say the suspect lives, roping off one home with police tape. In the middle of the day, only a dog's ferocious bark could be heard punctuating the stillness.

Sydney Carzola was in her early morning English class when the room fell quiet. She heard a pop from outside, in the school's quad. The noise wasn't unusual - students with later start times usually file into the building loudly, and Carzola thought someone had blown up a plastic bag and stepped on it.

"But then three consecutive pops went off right away," Carzola, a junior, said in an interview with The Washington Post. She knew it was a shooter.

EMBED: At least three students are injured, and two are dead after a 16-year-old student opened fire on Nov. 14 at Saugus High School in Santa Clarita, Calif.

Students ran into the classroom and barricaded the door with a computer cart. Some of her classmates were shaking and in tears. Carzola and others began considering ways to confront the shooter, perhaps throwing something at him.

"When I was in the situation, I didn't feel scared, and that's the saddest part," Carzola said. "I felt like everyone was going to go through this at some point and this was my turn."

Ryan Payad, a 14-year-old freshman, was across the street from the campus when he heard shots - and then heard screams pierce the air. He turned and ran, joining students fleeing the campus. He ran into his friend, Adolfo Ramirez, and the two spent time at Ramirez's house, reeling from what had transpired that morning.

"I'm just shocked right now," Payad said in an interview with The Post.

Ramirez, also a 14-year-old freshman, was blocks away from the school when the shooting happened. He was struggling to come to grips with how a shooting could take place at his school, in the heart of a suburb of Los Angeles.

"I never expected this to happen in the middle of a neighborhood like Santa Clarita," Ramirez said. "I felt protected."

Two female students told CNN in an interview that they heard five shots, one initial bang followed by four rapid shots. Voices shaking, the girls told CNN that students still inside the school hid in closets and texted updates to friends who had made it outside.

Another three students told the network that they were by the school library and saw a wave of classmates sprinting from the quad. They began running, too, leaving campus through a gate and rushing to the first house they could find in a nearby neighborhood.

They also heard five shots, and said they could immediately tell the bang they heard was not the sound of a popping balloon or a falling binder. They said it was a "gut feeling."

"It took us a minute to process that we needed to run," one of the female students said on air.

The girls said they knew it wasn't a drill because the school holds drills only after the school day has started. The mayhem unfolded as students were still making their way to class early Thursday morning.

Another student told KABC in an interview that she and other students huddled in an office when gunfire opened. The student said she texted her father to say, "I love you."

President Trump was monitoring the situation, according to a White House spokesman.

Sen. Kamala Harris of California, a Democratic candidate for president, spoke with CNN's Anderson Cooper live on air and called shootings at schools "the new normal."

"Our kids are living in fear, wherever they live, they are living in fear," Harris said. "This is yet again another reason why they are so afraid, that literally they will die. It's tragic in the most fundamental way. It is tragic. It is senseless. It is unnecessary. It is devastating."

Harris also called for "reasonable" gun-control laws in the United States. "Enough is enough," she said.

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Balingit and Mettler reported from Washington. The Washington Post's Mark Berman, Reis Thebault and John Woodrow Cox contributed to this report from Washington.

This article was written by Mia Nakaji Monnier, Crystal Duan, Moriah Balingit and Katie Mettler, reporters for The Washington Post.