Officials at the second largest school district in the United States asked parents to keep all 643,000 students at home to allow time for a full search of more than 900 schools. It was the first closure of the full district in at least a decade, officials said, and appeared to be unprecedented in scale.
The threat came less than two weeks after a married couple inspired by Islamic State militants shot dead 14 people in San Bernardino, California, about 60 miles (100 km) east of Los Angeles.
The school district regularly receives threats, but this one stood out for its scale, schools Superintendent Ramon Cortines said.
“This is a rare threat … It was not to one school, two schools or three schools, it was many schools,” Cortines told reporters at a press conference that began shortly before schools were to begin opening.
“I am not taking the chance of taking children any place into the building until I know it’s safe.”
Los Angeles police and the FBI were notified of the threat and were investigating, officials said.
The threat came via an electronic message and mentioned backpacks and other packages, Cortines said.
The threat was delivered to a school board member, the Los Angeles Times reported.
Students already at school were sent home, officials said, and families scrambled to come up with plans after the last-minute closure.
“It’s disappointing,” said Trinity Williams, a high school student who dropped off her younger sister at elementary school, only to find it was closed. The two traveled on to Williams’ high school before they realized the whole system was shut down.
“I was supposed to give an essay in class today, and finals are Friday,” Williams said. “I can’t afford to miss a day.”
Officials said they were not aware of any threats to schools in neighboring districts, adding that they would issue additional details on the Los Angeles threat later in the day.
School officials said that on Sept. 11, 2001, when many people returned home from work after the attacks on the East Coast, Los Angeles schools remained open.
The San Bernardino attack and other recent mass shootings have pushed the issues of militant Islam and gun violence to the forefront of the U.S. presidential campaign.
The United States has suffered repeated deadly attacks in schools in recent years, typically carried out by gunmen. The deadliest one in the past decade occurred at Virginia Tech, where a shooter killed 32 people.
The second deadliest left 20 young children and six educators dead at Sandy Hook Elementary School in Newtown, Connecticut in 2012.