A California high school student dressed in black is suspected of having opened fire on campus on Thursday, wounding at least five people and triggering a panic before he was wounded and arrested, officials said.
"Suspect is in custody and being treated at a local hospital," Los Angeles County Sheriff Alex Villanueva said on Twitter.
The female patient died at Henry Mayo Newhall hospital, according to hospital spokesperson Patrick Moody.
Moody said two male patients remain in critical condition, and one male patient remains in good condition at the hospital.
Before the sheriff's tweet, CNN reported that the suspect was dead, citing two law enforcement sources. The cable network later reported on the sheriff's "in custody" tweet and said the situation was fluid.
"We believe at this time that there is only one suspect but we are actively investigating and following all leads," the Santa Clarita Valley branch of the Los Angeles County Sheriff's Office said on Twitter.
The suspect was described by police as an Asian male and a student at Saugus High School in Santa Clarita, about 50 miles (80 km) north of Los Angeles.
A weapon was recovered at the scene, a police officer told NBC television.
The incident marked yet another school shooting in the United States, where repeated mass shootings in recent years have intensified the debate about gun control and the constitutional right for citizens to keep and bear arms.
Video from local NBC television showed a line of students walking away from the school and a row of police and fire department vehicles parked out front.
"I was really, really scared. I was shaking," one female student told NBC television, adding that she saw one person lying on the ground covered in blood.
The student said she was doing homework when people started running, and she hid under a table until police entered the building.
The mother of student Anthony Peters told NBC he was still on lockdown inside the school but had texted that he was uninjured.
"One of the teachers said, 'There is an active shooter. I heard the shots and saw three kids get shot,'" Peters' mother told NBC.
Some of the wounded were being treated in a grassy area on the school's campus, the Los Angeles Times reported. At least one injured person was found in the school's choir room, authorities told the newspaper.