A landslide triggered by torrential rain swept two buses off a road and into a river, killing at least 13 people and injuring 18, police said.
An unknown number of people remained missing after Monday's tragedy near the village of Caranavi, about 180 kilometers (110 miles) from La Paz, said Colonel Juan Cuevas, a traffic police official.
As rescue efforts continued, radio stations said the death toll was as high as 16 and could rise further because it is feared there are bodies buried by the landslide.
Around 10 people survived the accident.