Redwood High School in Larkspur was safely evacuated on Tuesday after the school reported a bomb threat, according to the school's Twitter account.
After the threat was reported, school and law enforcement officials announced that 1,900 students were "calmly leaving" classrooms and assembling at a safe location.
Students were not released until the entire school was evacuated, the Marin County Sheriff's Office tweeted.
Authorities advised that no injuries were reported.
Further information was not available.
Stay tuned for details.