Local police official Julio Larrea said there were "nine women, four men (and) a child" among the dead.
Larrea said the driver of the truck, which was loaded with salt, had veered across the road and hit the oncoming bus, reports BSS.
The accident occurred on a road linking the Andean towns of Oruro and Potosi.
"Lane encroachment, excessive speed and a lack of caution," caused the accident, another local police official, Adet Cabrera, told the TV channel Red Uno from the scene of the accident.
The driver of the truck, who survived the accident, was transported to a private clinic under police guard, according to Cabrera.
The bus was carrying 15 people, including the driver, who died in the accident.