Carlos Gonzalez, spokesman for the Chihuahua state prosecutors' office, said the driver appeared to have lost control of the truck after it leapt over a pile of cars it was crushing during a demonstration at the Extreme Aeroshow.
Some witnesses said the driver appeared to have hit his head on the interior of the truck as he drove over the old cars, with reports his helmet came off before the massive vehicle drove into the crowd of terrified spectators.
"I fell over and when I turned around I saw the tyre very close. It hit me and threw me to the other side," said Jesus Manuel Ibarra, 41, as he received treatment for injuries to his arm and hip.
Mr Gonzalez said Saturday's accident killed at least one child, and 46 people remained hospital early yesterday.
He said the number of dead and injured could rise.
Mr Gonzalez said prosecutors were looking into the possibility of a mechanical failure that left the driver unable to release the accelerator.
However, several witnesses said the driver appeared to have become incapacitated when he struck his head during the show, in which the truck drives at high speed over smaller cars, leaping into the air as it crushes their roofs.
The air show was cancelled after the accident, which happened during he second day of the three-day event in a park on the outskirts of Chihuahua, the capital of Chihuahua state.