No officers were injured in the incident.
Fontana Police Department officials said officers tried to stop an SUV about 3 p.m. in the residential area of Palmetto and Marygold avenues that had been reported stolen.
The driver allegedly refused to stop, then rammed a police car used to block him in to prevent him from fleeing.
Authorities said the officer inside the vehicle feared the driver was trying to kill him, so he opened fire to stop him. Multiple rounds were fired and the man was struck an unknown number of times, police said.
Some witnesses question the officer's actions.
"The car just tried to drive away, he was like 10 feet away, and the one cop on the passenger (side) got out and shot him like three or four times through the back window," witness Regina Mayorga said.
The suspect, whose name was not released, was pronounced dead at the scene.
Police said the suspect was the only person in the car.
No bystanders were injured.
The San Bernardino County Sheriff's Department is investigating the shooting.