Authorities decided to close the entire school system after it received a 'credible threat' of violence involving 'backpacks and packages' left at school campuses, officials said at a press conference yesterday.

Ramon Cortines, superintendent of Los Angeles Unified School District (LAUSD), said the shutdown was ordered after authorities alerted him to a threat "made to not just one school, but many schools in this school district".

The complete shutdown of public schools in Los Angeles come just days after the December 2 attacks in nearby San Bernardino by a Pakistani-origin couple that killed 14 people.

The Los Angeles Unified School District is the second largest school system in the US with more than 660,000 students in kindergarten through 12th grade and 250,000 in adult education program.

The Federal Bureau of Investigating is looking into the threat and still analysing it.

Schools would remain closed until the threat was cleared, which could happen by the end of the day, officials added.

Yesterday, classes were also cancelled at San Bernardino Valley College because of a bomb threat and staff and students were sent home in the evening.

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