Two of protesters were injured but one of them was taken to hospital.
The group of protesters had gathered ahead of Trump’s visit to Sacramento where he gave a briefing on the escalating wildfires which have ravaged California, and other states, in recent weeks.
At approximately 1pm local time, near Sacramento’s McClellan Airport, a protester could be seen crawling on the hood of the police car, scaling the windshield when, without warning, the car accelerated rapidly, sending the man and several of his fellow protesters flying.
Two people were injured in the incident, with the man thrown over the hood of the car taken away on a stretcher to a nearby hospital for treatment. His injuries are not thought to be life threatening.
Footage of the incident quickly went viral, sparking a slew of insults and taunts as well as memes online.
It was the second such incident involving a vehicle striking anti-Trump protesters at the scene.
Earlier in the day, a green Volvo, believed to be a civilian vehicle, reportedly drove into a group of protesters.