The incident, in which 10 cattle were also injured, occurred when the truck overturned at a steep curve near Kanhauli mor, Mahua police station Officer-in-Charge Shashi Bhushan Kumar said.
The injured cattle were being attended by veterinary doctors at a nearby hospital, he said.
The truck, which was on its way to Hajipur from Samastipur, has been seized by police, while its driver managed to flee from the spot, Kumar added.