The incident was reported at about 7:48 p.m. in the 13500 block of Foothill Boulevard, according to the Los Angeles Police Department.
Police said the officer was investigating a traffic collision when he was struck by a vehicle.
The officer was taken to a trauma center in serious condition, according to the LAFD.
LAPD described the incident as a possible hit-and-run.
An arrest has not been announced. Meanwhile, an investigation centered on a neighborhood in Pacoima where dozens of officers surrounded a home.
Further details were not released as the investigation continued.
This is a developing story. This article will continue to be updated as more information becomes available.