The accident took place near the Cold Storage Chowk under Tajpur police station area when the truck driver hurriedly applied brakes on seeing a tractor in front of his vehicle.
The truck overturned and fell on the four who were walking by, Superintendent of Police Nawal Kishore Singh said.
All four died on the spot.
Efforts are on to ascertain the identity of the victims, he added.
The truck driver fled from the spot.