Two teenagers are dead after a 16-year-old boy opened fire at a high school in California, leading to a high-intensity manhunt through the suburban streets of Santa Clarita, a community in shock after early-morning violence has rocked the neighbourhood.

The suspect entered the Saugus High School campus just after 7.30am, then quickly removed a .45 calibre semi-automatic pistol from his book bag and fired at a group of students, striking five before turning the gun on himself. He is in "grave condition" at a local hospital after surviving a gunshot wound to the head. Police say that today is his birthday.

Los Angeles FBI Agent Paul Delacourt said authorities "have no indication of any motive or ideology".

A 14-year-old boy and a 16-year-old girl taken to a local hospital in critical condition later died.

One male student remained in critical condition, while a fourth patient, a 14-year-old boy, was hospitalised in "good" condition.

Two girls, ages 14 and 15, also were hospitalised.

Santa Clarita school shooting Show all 20 1 /20 Santa Clarita school shooting Santa Clarita school shooting Students are escorted out of Saugus High School after reports of a shooting AP Santa Clarita school shooting At least six people have been injured following reports of a shooting at the school, roughly 40 miles north of Los Angeles in Santa Clarita KTLA Santa Clarita school shooting Students are comforted as they wait to be reunited with their parents AP Santa Clarita school shooting Paramedics transport an injured person AP Santa Clarita school shooting Students get on a bus after the shooting AFP via Getty Images Santa Clarita school shooting Police search a home in connection with the shooting AP Santa Clarita school shooting Students are escorted out of Saugus High School AP Santa Clarita school shooting D J Hamburger, center in blue, a teacher at Saugus High School, comforts a student AP Santa Clarita school shooting People are lead out of Saugus High School after reports KTTV-TV via AP Santa Clarita school shooting Women embrace in Central Park after the shooting AFP via Getty Images Santa Clarita school shooting People wait outside of Saugus High School after reports of a shooting on Thursday, Nov. 14, 2019, in Santa Clarita, Calif. Los Angeles County Sheriff Alex Villanueva tweeted that the suspect was in custody and was being treated at a hospital. He said the suspect was a student but gave no further information.(AP Photo/Marcio Jose Sanchez) Marcio Jose Sanchez AP Santa Clarita school shooting Students line up after a shooting AFP via Getty Images Santa Clarita school shooting People wait for students and updates outside of Saugus High School AP Santa Clarita school shooting Ambulances parked outside of Saugus High School AP Santa Clarita school shooting Law enforcement personnel gather outside Saugus High School AP Santa Clarita school shooting The sheriff's office says a male suspect in black clothing was seen at the school NBCLA via Reuters Santa Clarita school shooting A law enforcement official leads students at the scene VIA REUTERS Santa Clarita school shooting Police are searching for a 15-year-old suspect KTTV-TV via AP Santa Clarita school shooting A law enforcement official leads students at the scene VIA REUTERS Santa Clarita school shooting Police are searching for a 15-year-old suspect following a shooting at a high school in Santa Clarita, California.

Another victim who was not wounded by gunfire was sent to another hospital with non-critical injuries. All the victims are students.

Police and hospital officials have not revealed the hospital where the suspect remains in custody.

"In the days ahead, in the years ahead, the main thing we need to do is wrap our arms around one another", said Santa Clarita Sheriff's Office Capt Robert Lewis. "We need to say, 'No more.' ... This is a tragic event that happens too frequently."

After the suspect opened fire, dozens of students escaped campus, or ran into classrooms where to hide in closets, where they frantically texted friends and family while waiting for police to clear the area.

In texts shared with The Independent, the parent of a 14-year-old 9th grader told their child not to panic as they remained on lockdown inside the school.

Police said there were no more bullets left in the suspect's gun after it was recovered. Abandoned papers, binders and school bags were scattered throughout the school's quad where the shooting took place.

The shooting was captured on school surveillance footage, which authorities will "pick apart", according to Santa Clarita Sheriff Alex Villaneuva.

"I hate to have Saugus be added to the names of Columbine, Parkland, Sandy Hook, but it’s a reality that affects us all across the nation," Mr Villanueva said.

Off-duty police were the first to respond to the scene. A detective was dropping off a child at the school and was able to respond "literally, within seconds", Mr Villanueva said.

Parents waited for their children at a designated reunion area at a nearby park, where hundreds of students made emotional reunions with their families.

Aerial news footage showed lines of students being escorted from the school by armed sheriff's deputies, while several people were being removed from campus on gurneys. At one point, emergency services could be seen giving CPR to a victim on the lawn outside the school.

Following a search, a Swat team captured the suspect — described as an Asian male wearing blue jeans, a black hat and black shirt — and sent him to a local hospital, where he is being treated while in custody, according to police.

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Residents of nearby homes were told to lock their doors and stay alert for the suspect.

Armed officers were seen shutting off roads and surrounding homes in their search for the suspect.

At one point, police closed down a highway and lined up close to a tree, after reports that the suspect may have been hidden in undergrowth.

But they were quickly stood down and moved on to surrounding neighbourhoods where houses were methodically surrounded.

Capt Wegener says a search warrant has been issued and police are currently investigating the suspect's house, on a quiet, tree-lined street in an area that neighbours described as ordinary.

He says a message on the suspect's Instagram account — "Saugus, have fun at school tomorrow" — has been verified, but it was changed, meaning someone else has access to the account.

One neighbour told local news outlet KTLA that the suspect's father recently died.

Mayor Marsha McLean, whose granddaughter attends the school, said Santa Clarita is "a close-knit, family-oriented community."

"When I heard about it, the feeling that went over me was indescribable", she told reporters.