All the four died on the spot while the driver fled away, police said.
Locals rushed to the spot to help the victims but all of them had already died. The bodies were taken to Anugrah Narayan Magadh Medical College and Hospital (ANMMCH) at Gaya for postmortem examination.
Belaganj SHO inspector Vinay Krishna Prasad said the truck has been seized and search is under way to arrest the absconding driver.