Authorities say an explosion at Hillsdale High School in San Mateo has forced students to leave and classes to be canceled. There are no reports of injuries.

San Mateo police Lt. Mike Brunicardi says officers received several calls just after 8 a.m. Monday from teachers and staff reporting some kind of blast.

Brunicardi says students were evacuated immediately to a nearby middle school.

A bomb squad is searching the school for any other explosive devices.

Hillsdale High School is starting its second week of classes for the new school year. It has 1,200 students.