The bus turned onto one side and the ground blocked its exit doors, said Roberto Hernández, the civil defense director for Nogales township.
Initial reports said 20 people were killed, but state civil defense director Guadalupe Osorno said one injured person died later.
Authorities said both vehicles were westbound when they apparently collided in a mountainous area known as Cumbres de Maltrata. Both caught fire.
In April 2006, a bus carrying religious pilgrims in the same area ran off the highway and tumbled down a steep ravine, killing 65 people.
Copyright 2019 The Associated Press.