All Los Angeles Unified School District schools were closed Tuesday after LAUSD received a "credible terror threat," according to school district officials and police.

The Los Angeles Police Department told KTLA that the threat prompted the decision from LAUSD Superintendent Ramon Cortines to close all schools until further notice.

The threat, which was against "many schools," was received electronically and mentioned backpacks and other packages, Cortines said at a morning news conference. The nature of the threat was "unspecified."

Cortines has ordered all schools be thoroughly searched to ensure the grounds were "safe for children."

LAUSD is the second largest school district in the country, serving more than 640,000 students between kindergarten and 12th grade, according to its website. There are more than 900 schools and 187 public charter schools in the district.