More than 640,000 students were affected. Parents were told not to send their students to school in a statement by the superintendent made just after 7 a.m. Tuesday.
The threat was sent electronically and only referenced Los Angeles-area schools. It mentioned backpacks and other packages, but the exact nature of the threat was "unspecified," LAUSD Superintendent Ramon Cortines said at a morning news conference. Authorities were still analyzing the threat and all Los Angeles law enforcement agencies were working together to search every school in the district, he said.
"I've asked the plant managers to walk the school, and if they see anything that is out of order to contact the police," Cortines said.
Cortines said he felt the precautionary closures were necessary because of the recent mass shooting in San Bernardino.
There have been no threats to San Diego school, according to the San Diego Unified School District, but district officials are in contact with Los Angeles school officials and San Diego school police are increasing security patrols as a precaution.
Check back for updates on this developing story.