An investigation is underway in Azusa, where fire officials say three to five people may be injured in what police described as an active-shooter situation.
Los Angeles County sheriff's deputies and and firefighters responded shortly after 2 p.m. to the area of Fourth Street and Orange Avenue, after Azusa police officers were shot at in the area and a call for help was made.
A staging area and perimeter were established, as several neighboring law-enforcement agencies went to the scene to assist.
Slauson Middle School was on lockdown, school officials said, adding that students would not be released from campus until an "all clear" was given by police.
DEVELOPING: More details will be added to this report as they become available.