The mishap took place on the National Highway when the car, ferrying six persons, was on its way to Sitapur, they said.
Three persons, identified as Gajodhar (70), Veerendra (25) and Sunny (4), died on the spot, police said, adding that the injured have been rushed to a hospital in Sitapur.
A hunt has been launched for the bus driver, who fled from the scene.