“The vehicle was hit by 18 bullets,” presidential spokesman Juan Manuel said.
Another person was injured in the shooting, said a police officer on the scene.
The motive of the shooting was not clear.
President Alvaro Colom’s office said in a statement that authorities were investigating whether the shooting of the 74-year-old singer was robbery-related or a targeted attack.
Cabral, who was popular in Latin America, had been in Guatemala on tour.