The FBI and explosive experts have been called in to sweep every locker, classroom, office, and bathroom of every campus across the 5,000-square-mile county.
Ramon Cortines, superintendent of Los Angeles schools who made the decision to close all 900 institutions, told a press conference at 7am Pacific Time he had received an email describing plans to bomb at least three schools and multiple students.
This is not the first threat made against the district but this instance is unique, he said.
However, he insisted he is acting out of 'an abundance of caution' in light of the recent attack on the neighboring city of San Bernardino, Daily Mail reports.
Steve Zimmer, president of the school district board, urged: 'Parents, if you have not sent your kids to school, do not send them to school.'
He said searches will start on all 900 campuses this morning and will be completed within the day.
'It's going to be a long day,' he added.
Students who had already arrived at school were sent to specific gates to be collected by parents or guardians.
Parents picking up their children have to bring 'proper ID', the school district said.
A terror expert speaking on CNN surmised that the person or people who made the threat have already achieved most of their objective: instilling terror in the city - and indeed that nation.
'Whoever's put this threat out will be watching this coverage with great satisfaction,' he said.