CIUDAD JUAREZ, Mexico (AFP) - The driver of a monster truck that ran over spectators in northern Mexico had performed an unsanctioned stunt in the tragedy that killed eight and injured 87, a governor said Monday.

At least 29 people remained in hospital, including 13 in intensive care, following Saturday's accident at the demolition show in Chihuahua, capital of the eponymous state, said Governor Cesar Duarte.

Four of the eight fatalities were children.

The 51-year-old driver, Alfredo Velazquez Samaniego, who is being treated for a head injury at a hospital, was detained and prosecutors said he could face manslaughter charges.

But authorities are also investigating the safety measures that were put in place by organisers at the Extreme Aeroshow, which was sponsored by the municipality.

Video footage show the monster truck leaping over two crushed cars, landing on its giant front wheels and bouncing before plowing into a nearby crowd of spectators who were not behind security barriers.

Mr Duarte said the driver had made an unauthorised maneuver by making another pass over the two cars in the opposite direction, which had a much shorter distance between the stunt and the spectators.

Velazquez Samaniego also admitted that he had consumed two beers before getting behind the wheel of his truck, though a blood alcohol test showed that he was not drunk, Mr Duarte said.

"The fact that he drank and the statements he made show a lack of expertise and a direct responsibility in the handling of the vehicle," the governor told Milenio television.

The driver said he lost consciousness after hitting his head in the landing and footage suggests he accelerated after passing over the cars, he said.

"We have a meticulous investigation that we want to conclude, and will then determine where responsibility lies," Mr Duarte said.