Te Puke A & P Association president Murray Jensen said the "unfortunate freak accident" happened while the girl was standing on the back of the ute parked under some trees.
Jensen said the toddler had been watching the Truck and Tractor Pulling Competition when the ute tailgate suddenly came open, and the girl hit her head as she fell from the vehicle.
"I saw a St John ambulance arrive but initially thought it was in response to some kind of minor medical event until I saw the police also turn up," he said.
Jensen said he understood the girl was unresponsive at first but by the time the ambulance arrived at the showgrounds she had regained consciousness.
"The girl's parents were also at the show and were comforting the child ... I saw her mother sitting in the back of the ambulance with her daughter at one stage," he said.
Jensen said it was upsetting matter for everyone including the show organisers.
"We have had a few medical events during the show from time-to-time and once a motorbike rider had to be taken to hospital but nothing this serious before."
Jensen said most of the show was starting to wind up when the accident happened.
"I not sure whether the little girl opened the tailgate or it wasn't latched properly, but it's the last thing we wanted to happen ... I just hope she is okay."
Jensen said it appeared to be a frontal head injury.
"There was no blood as such but clearly there is always a major concern about concussion, particularly when it is someone this young," he said.
Another man who attended the show, who asked not to be identified, told the Bay of Plenty Times that the accident happened while he was competing in the truck and tractor pulling competition.
"I didn't see the girl fall but once I saw the ambulance and fire engine screaming in naturally we were all very concerned, especially as the little girl was unconscious at first."
The man said the competition was immediately halted to make room for the TECT rescue chopper to land and it did not resume until about 5pm, he said.
The Bay of Plenty Times was not able to contact the girl's family for comment.