Two victims – a 16-year-old girl and a 14-year-old boy – died of their injuries, police said. The other victims were two girls aged 15 and 14, and a 14-year-old boy.

The suspect was “identified as a 16-year-old male whose birthday was today”, firearms expert Captain Kent Wegener said. He was named by US media as Nathaniel Berhow.

The Associated Press quoted a fellow student, Brooke Risley, as saying he was introverted but “naturally smart”, adding that he had a girlfriend and was a boy scout.

According to surveillance footage, the suspect took a gun out of his backpack and shot the five students, before shooting himself in the head, Mr Wegener said.

The weapon recovered was an emptied .45 calibre semi-automatic pistol, he added. Police said they had located the suspect’s home and would search it for evidence.

What was it like for other students?

Saugus High School and other neighbouring schools were placed on lockdown during the shooting. The lockdown was lifted about three hours later.

LA undersheriff Tim Murakami wrote on Twitter that police would be interviewing all Saugus High School students before releasing them to their parents. He added that they would investigate rumours that the suspect had posted threats on social media.

One student told NBC she was doing her homework when people started running. “I was really, really scared. I was shaking,” she said.

Another student, named as Azalea, told CBS she and her classmates had barricaded the classroom door with chairs. “It was just really scary, having everybody panic and call their parents, saying they love you.”

News of the attack emerged during a Senate debate on gun control legislation. Senator Richard Blumenthal, a Democrat, was arguing for gun control when he was given a note with the news.

“We are complicit if we fail to act,” he said. “It is not just a political responsibility, it is a moral imperative.”

Meanwhile, the acting Homeland Security Secretary, Chad Wolf, said in a statement that his department took school shootings “very seriously” and would help the authorities “develop trainings and resources to improve response capabilities and better protect soft targets”.

Gun control, and the right to bear arms, is a divisive political issue in the US. About 40% of Americans say they own a gun or live in a household with one, according to a 2017 survey, and the rate of murder or manslaughter by firearm in the country is the highest in the developed world.

According to the Washington Post, more than 230,000 young people in the US have experienced gun violence at school since the Columbine High School massacre in Colorado in 1999.