The prosecutors'office in the northern border state of Sonora said the driver of the bus had apparently tried to outrun the train at a grade crossing. The driver survived and was taken into custody for drug and alcohol testing.
The office said the dead included five men ranging in age from 16 to 30, a woman and a 16-year-old girl, AP reported.
The statement said 32 people had been received at the General Hospital in Ciudad Obregon as of mid-afternoon. Four more were treated at a social security clinic in Cajeme.
The state Civil Defense Department published images of white-vested Mexican Red Cross workers attending to victims as the white bus lay battered along the tracks.
A medical helicopter and ambulances were dispatched to the scene of the crash in Vicam, near Guaymas.
Local media reported the bus had been dragged 20 yards (20 meters) after the collision with the train.