Los Angeles has closed all public schools after an unspecified bomb threat, according to local reports.

The Los Angeles Unified School District (LAUSD), the second largest in the US, confirmed the shutdown and said it received an electronic threat that mentioned backpacks and other objects. Students and staff have been sent home on 15 December and they were told to stay away from campuses.

LAUSD Supt. Ramon Cortines explained that the threat was made "to many schools" not a specific one. "We have received an electronic threat. That threat is being analysed. We closed schools to make sure campuses are safe," the official said.

The decision comes less than two weeks after two gunmen killed 14 people in San Bernardino in what was the deadliest terrorist attack on US soil since 9/11. "I am not going to take a chance with the life of a student," Cortines said, adding that LA schools get threats all the time but this is a "rare threat".

The FBI is assisting Los Angeles police in the schools' investigation, according to CBS News.

Authorities plan to search all of the LAUSD's schools before opening them, Los Angeles Times reported.

The district, the second largest in the nation, has 640,000 students in kindergarten through 12th grade and more than 900 schools and 187 public charter schools.

The district spans 720 square miles including Los Angeles and all or part of more than 30 smaller cities and some unincorporated areas.