Rodeo parade spectators watched in horror Thursday as a 5-year-old girl — three years younger than the event's minimum age — was thrown off her mount and trampled by an out-of-control team of horses pulling a wagon. She later died.

Hundreds of people were in eyesight of the tragedy along the two-mile route of the Tucson Rodeo Parade.

"I saw the wagon coming around the corner out of control," said Henry Hebert, who was near the scene of the accident. "They hit the horse, her horse flared up and the girl fell off."

Hebert said it appeared two other girls riding beside the 5-year-old saw the horses coming at them and were able to get out of the way. Witnesses differed on whether the wagon ran over the victim.

The girl, identified as Brielle Boisvert, died less than 30 minutes after the accident at University Medical Center, hospital spokeswoman Darci Slaton said.

Pastor Marc Hill of Benson, Ariz., one of two clergymen representing the family, said that Boisvert's family blames no one for the accident.

The child was one of four riders from Sonoita Rodeo Royalty and was riding her own horse, said Robert Johnson, a spokesman for the Tucson Rodeo Parade Committee.

The death was the first in the parade's 85-year history although injuries at the event are not uncommon, Johnson said.

At last year's event, Mayor Bob Walkup bruised an arm and his wife, Beth, suffered a concussion and whiplash when two runaway horses slammed into the rear of a 150-year-old buggy.

The parade, which is insured, is billed as the world's longest non-mechanized parade and includes horses, marching bands, folklorico dancers and beauty queens. It is one of the highlights of the 82nd annual La Fiesta de los Vaqueros rodeo, a weeklong event that began Monday featuring more than 700 contestants from across the U.S. and Canada.

Johnson said some horses are trained before the parade in the presence of fire trucks, sweepers, vans and buses, with noise including sirens and music. The girl's horse was not among those so trained although the horses pulling the wagon had gone through such practice sessions, according to Johnson.

Tucson Police Chief Richard Miranda said investigators were interviewing witnesses and others — including the driver of the wagon — to determine what happened and whether there could be criminal charges.

Johnson acknowledged that the girl was three years younger than the age limit stated in the parade's online entry form. He said all entrants sign waivers to participate in the parade and there are no monitors to confirm ages.

Walkup said he and the City Council will decide the parade's future in light of the latest accident.