State attorney general's spokesman Fernando Hidalgo says the accident happened yesterday as a group of tourists was returning to Mexico City from a weekend trip to the thermal baths in the town of Santa Maria Amajac.
Hidalgo says witnesses reported that the bus driver lost control when the vehicle blew a tire. The bus hit a guard rail and flipped.
The official says the bus was an old model from the 1970s and in poor condition.
The attorney general's Twitter account says seven men, seven women and two children died. Nineteen people were injured.