Kailash (50), his wife Vandana (45), son Manish (25), driver Akash (35) were killed on the spot, SP (Rural) Jagdish Sharma said.
The mishap took place last night on NH-24 and the police are trying to trace the vehicle which hit the car.
Condition of Rinki, daughter of Kailash and Vandana, is stated to be critical, he said, adding that the bodies have been sent for post-mortem.