At least 16 youngsters were killed and 32 injured when their bus plunged into a 400ft ravine north of Bolivia's capital La Paz on the way to a school sports event.
Transit police chief Victorino Torres said the death toll could rise because rescuers were still searching the wreckage in the Acero Marka district.
Mr Torres said the students were aged 16-18 and were travelling to La Paz to compete in an inter-school sports competition.
He did not say what caused the accident, but survivors said the driver tried to let another bus pass on the narrow road, then went into the ravine.
Hospital official Fernando Arispe said some of the 32 injured were in a "very serious" condition.
:: A bus packed with French tourists collided with a train in the eastern Dominican Republic, killing at least three people.
At least 10 passengers on the bus were injured when it hit the train and were taken to nearby hospitals, said Amado Avila, director of the civil defence agency for La Altagracia province.
The two men and a woman who were killed were French citizens, he said.
Nearly 30 French tourists were on board the bus along with two Dominicans. It was coming from the airport when it struck the train, operated by a local sugar company near the town of San Rafael del Yuma, about 100 miles east of Santo Domingo.
The tourists were apparently heading for the Punta Cana resort complex.