The accident happened around 3 p.m. Thursday near Unduavi, El Diario, of La Paz, Bolivia, reported.
The bus, owned by Eugene Arenas Aliaga Irupana, was heading to Entre Rios when it veered off the road and plunged 393 feet off a cliff, making it difficult for rescuers to reach the occupants immediately, the report said.
What caused the bus to veer off the road was not reported.
Many of the 18 who died were young people between the ages of 15 and 17 from the Education Unit of Chicaloma, officials said,
Those injured were brought to a hospital where doctors said at least two were in critical condition.