The driver of the truck, laden with iron rods, lost control of the vehicle and crashed into the railing of the bridge, causing the structure to break down almost instantly, he said.
The truck fell into a ditch, killing two of its riders. Rescuers have recovered one dead body, but another body was still trapped inside the truck, said Alam.
Another five, who were also in the truck, were rescued alive by locals. They have been admitted to the Sunamganj Sadar Hospital with injuries.
The police and fire fighters are working to salvage the truck.