Police say the boy was involved in the melee and fell into the path of a truck that was being driven along the internal access road.

He was seriously injured when he was run over by the rear wheels of the trailer and was taken to Wagga Base Hospital. He is expected to be airlifted to Sydney for treatment of a fractured pelvis, internal injuries and serious leg injuries.

The truck driver, a 39-year-old man, was uninjured during the incident but also taken to hospital for mandatory blood and urine tests.

A crime scene has been established inside the Urana Street entrance to the venue and a number of people could be seen standing outside the gates last night. 

At least four ambulance vehicles and six police cars were on scene.

Another ambulance was called to treat a male, believed to be in his 30s, for a possible broken nose and other injuries.

Investigations into the incident are continuing.