It happened Sunday just before 9 am on Lerdo Highway east of Cherry in Shafter, located north of Bakersfield.
CHP officials say the officer was responding to another collision, standing near the open trunk of his patrol car with the emergency lights on.
That's when a woman in a Honda Accord hit the patrol vehicle. It's unclear if the officer was hit by Honda or his own car, but he was taken to the hospital with major injuries.
Officials say visibility in the area was low because of heavy fog.
The CHP said drugs or alcohol were not factors in the crash.