The accident in the city of Chihuahua on Saturday also left 67 people injured, sharply up from the 47 authorities originally reported.
Two people died early Sunday after six were killed almost instantly Saturday, said Carlos Gonzalez, a prosecutor's office spokesman in Chihuahua.
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Chihuahua State Governor Cesar Duarte said that 12 of the injured were in critical condition. Mechanical failure was among the hypotheses being considered as cause for the incident, he said.
Gonzalez said a driver was being questioned as well.
Some 3,500 people attended the demolition show, in which pick-up trucks with giant tires crush smaller cars, when the vehicle lost control and smashed into the packed stands at around 7:00 pm.
It was part of a third annual air show, which attracts 200,000 people on average and includes airplane stunts, skydiving and motorcycle acrobatics among other daredevil acts.
