It was not immediately clear how many people were on board the bus.
Authorities said their initial theory was the crash was caused by speeding, with the driver “unable” to control the bus, according to Benavides.
This is the most serious road crash reported in the South American country so far this year.
Nineteen people were killed when a bus careened off a road, also near Potosi, last month.
Bolivia’s winding mountain roads are notoriously deadly.
Road crashes kill an average of 1400 people every year in the country of about 12 million inhabitants, according to government data.
- Agence France-Presse