Police say the vehicle crashed when it tried to pass a tanker truck on Monday.
A bus fell 200 meters into a ravine, leaving 25 people dead after a collision involving two trucks, Bolivian police said on Monday.
Interior Minister Carlos Romero said the bus driver tried to pass a tanker truck, collided with another vehicle and then tumbled down a 300-metre (roughly 1,000-foot) deep ravine in the northern town of Yolosa, 80 kilometres (50 miles) north of the capital, La Paz.
"That's why the vehicle lost control and went over the cliff (falling) 200 metres," said La Paz, police chief Yuri Calderon, who initially gave a death toll of 17.
Highway patrol chief Fernando Rojas, cited by Fides news agency, revised that number soon afterwards.
"We're recovering the bodies, we're talking now about 25 confirmed dead and 24 injured, who have been transferred to various hospitals," said Rojas.
'Be very careful'
Bolivia's President Evo Morales, who is visiting Argentina, pleaded on Twitter for bus drivers to take more care.
"Very sad about the terrible accident that happened on the La Paz-Yungas road," he wrote.
"Our condolences to the relatives of the deceased. To our brother drivers we ask you to always be very careful; taking care of life is the most important thing."
Calderon said firefighters were working at the scene.
Rescuers descended the precipice on a rope and brought up the victims and survivors one by one, television images on the Unitel channel showed.
The destroyed bus could be seen at the bottom of the ravine.
The bus, operated by Totai, was travelling north from La Paz, the administrative capital, to the Amazon town of Rurrenabaque.
The death toll makes this the most deadly bus accident this year in a country that has a sorry record for highway safety.
In January, 22 people died when two buses collided on the road between the southern regions of Oruro and Potosi.
The very next day, 12 people died after a bus careered over a cliff edge near the south-central city of Sucre, the historic capital of Bolivia and seat of the supreme court.
And in February, 24 people died in an accident between a bus and a truck in Oruro.