The Brentwood High School in California was on lockdown Thursday morning after a gunman entered the building.
A spokesman for the school said students and staff were taken to a different building after a lockdown was lifted.
Brentwood police Chief Anthony Salerno said the lockdown is temporary and students and teachers can return to class if they feel safe.
He said Brentwood is working with the FBI and local law enforcement agencies to identify and detain the shooter.
Authorities say the shooting occurred inside Brentwood’s Brentside High School, where several people were shot in the school, including two students who were shot dead.
One student who was shot in Brentwood, identified by CBS Los Angeles as a senior high student, was in critical condition Thursday.
A fourth student was in serious condition and was expected to survive.
The school was placed on lockdown and police closed it to the public until the investigation was complete.
It was not immediately clear what sparked the lockdown, but police said it was an isolated incident and that no students or staff were injured.
Bryan M. Hall, who teaches at Brentwood Community College, said he heard at least five gunshots near his classroom.
He said the gunman was not a Brentwood student.
We are all very shaken up,” Hall said.
Hall said he doesn’t think the shooter had anything to do with the shooting.
“There is nothing to connect this to this school,” Hall added.
A spokesperson for Brentwood Elementary School told ABC News that all students were safe and accounted for.