A threat at Northwood High School in Irvine triggered a lockdown Thursday afternoon, school officials said.
The Irvine Police Department said it received a call about 1:40 p.m. from a man threatening violence on the high school campus. Officers immediately responded to the school and were working with the school's staff "to ensure the safety of the students," police said.
"There has been no suspicious activity noted on campus and no injuries," police said.
The Orange County Sheriff's Department bomb squad and helicopter were assisting police, said Jaimee Blashaw, a sheriff's spokeswoman.
Annie Brown, spokeswoman for the Irvine Unified School District, said the school was placed on lockdown "out of an abundance of caution."
"Instruction is continuing while the police investigation is going on," she said. "School is out at 3:30 p.m."
3:25 p.m.: This article was updated with police saying no suspicious activity was found on campus.