Two students have been killed and three others injured by a 16-year-old who opened fire at a secondary school in California, officials say.
The shooting took place at the Saugus High School in Santa Clarita, north of Los Angeles, minutes before the school day was due to begin.
The male suspect, who was also injured, is now in custody.
Many US schools have implemented active shooter drills in recent years, following a string of attacks.
- America’s gun culture in charts
- What do US Democrats want to do about guns?
What do we know about the attack?
The shooting was first reported at 07:38 local time (15:38 GMT), LA county sheriff Alex Villanueva told a press conference.
“Within seconds we received multiple [emergency] calls,” he said, adding that the first police units had arrived at the scene within two minutes.
Police found six people suffering from gunshot wounds and transferred them to local hospitals – and the suspect was later identified as one of those injured, Mr Villanueva said.
Two victims – a 16-year-old girl and a 14-year-old boy – died of their injuries, he added.
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”, he added.
According to witnesses, the suspect took a gun out of his backpack and shot the five students, before turning the gun on himself.
The weapon recovered was an emptied .45 calibre semi-automatic pistol.
Police say they have located the suspect’s home and will be searching it for evidence.
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.”
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.
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.