The Santa Clarita Valley Sheriff's department had warned residents to stay clear of the area.
A gunman opened fire at a California high school killing a 16-year-old girl and a 14-year-old boy, officials say.
A 16-year-old suspect wounded three other teens before shooting himself. "If you see suspect, male dark clothing, in backyards, etc. CALL 911", the Santa Clarita Valley Sheriff's Station announced on Twitter.
"Among those that were transported turned out to be the suspect, who is now in the hospital in grave condition", said Los Angeles County Sheriff Alex Villanueva.
Investigators said they did not know what led the student to open fire at the school 40 miles (65 km) north of Los Angeles. Three males and one female were injured, according to the hospital.
Classes were in session at the time, but some students were outside, officials said.
A 16-year-old girl died at a hospital.
"It's a tragedy every way you look at it, but there's a silver lining behind this: the fact that off-duty first responders were there and did not hesitate ... and they rendered first aid immediately", the sheriff said.
A 14-year-old boy was treated and released from another hospital, authorities said.
Teresa Figueira, a student at the school, said: "I was walking with my sister and we were walking into school and then I heard a shot".
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The suspect is believed to be a student at the school, Los Angeles County Sheriff Alex Villanueva told CNN affiliate KABC. Two males are still in critical condition and the other male is in "good condition".
Student Alexa Funk, 15, recalled hearing the first shot, and the second, but did not get scared until the third bullet was sacked. He is being treated for a self-inflicted gunshot wound to his head. I'm pinned in a room.
He said that authorities received a call at 7:38 a.m. about a shooting at Saugus High School.
Now, as the community wades through the chaos and grief, authorities are desperate for answers.
"We have not yet established a motive or a nexus between the subject and his victims other than to say that they were all students at the high school together", Wegener said. Police said he turned 16 on Thursday. The message said: "Saugus, have fun at school tomorrow". "That was posted at one point". Several injured. LASD resources on site and searching for suspect.
The suspect's girlfriend and mother were with authorities.
School district spokesman Dave Caldwell told the station all campus lockdowns in the district have been lifted except for Saugus High.
They "encountered in the quad area of the school multiple victims with gunshot wounds".
"Kids said there was a shooter, so we pushed all the desks up against the door, and barricaded ourselves in", he said.
"Yet today, our brilliant staff bravely and vigilantly went into action", Kuhlman said.