Mario Cruz, the spokesman for the volunteer fire department in the area, said another 45 injured people had been taken to hospitals.
Cruz said about 80 people were aboard the bus, which had been headed for Guatemala City. The dead included at least three babies.
"Some of the people were rescued with hydraulic equipment, and others were thrown (from the bus) at the time of the accident," Cruz said.
Volunteer firefighter Juan Pablo Ucla said the bus fell into a river at the bottom of the 600-foot canyon around 8:15 AM (local time).
