A police officer said all the deceased were travelling in the autorickshaw which came before the bus and the heavy vehicle rammed into it, killing five occupants on the spot.
Nine others were injured in the mishap, some of them severely, the officer said, adding that the injured are from both the vehicles.
The deceased included two women and a child.
The private bus was travelling from Raiganj to Buniyadpur while the auto was on its way to Balurghat when the mishap occurred near Mohagram bus stop along Raiganj-Balurghat State Highway. The injured were taken to a nearby hospital.