A pedestrian was critically injured when he was absolutely plowed by a police cruiser while walking in a crosswalk in the Los Angeles area this weekend ... and the moment was all caught on video.

Check out the footage -- the man is in the crosswalk as the traffic light appears to have changed ... with other cars already rolling by ... he's nearly to the sidewalk when he looks up and starts to trot -- and then he's blasted by a fast-moving Montebello Police Department patrol SUV.

The impact sends the victim flying through the air as he lands yards away ... while the patrol car veers and smashes into the traffic light pole. The dazed officer inside takes a few moments to collect himself before jumping out and running over to the injured man ... other cars stop and one driver gets out to render aid.

California Highway Patrol tells TMZ the unidentified pedestrian was rushed to a hospital with major injuries. He was listed in critical but stable condition. The officer was taken to a nearby medical facility for minor injuries.

CHP adds police were responding to a report of a possible DUI driver in the area -- and the cruiser that hit the man was one of the units racing to the call.

CHP is investigating the incident.