A video of the incident showed the rogue fireworks landing in the crowd to shrieks and panic.
Robertson said he had collected one of the clay-like plugs and described it as the size of a stack of 10c pieces.
“I’m not sure what has happened but it is a clay-type insert that must hold the charge.”
“I’ll find out from the manufacturer what has gone on. It is the same supplier I have always used in the past.”
Privately-hired medical staff treated people at the event, with one man saying the paramedic who saw his son had already treated seven people.
The man was sitting with family and friends, including children, when a fireball hit a child next to them and then hit his friend’s daughter.
“It was a bit of a double whammy because we were dealing with that and then our boy got hit in the forehead - all the kids were terrified,” the man said.
The man said it was lucky it didn’t hit him in the eye.
“It didn’t break the skin but he had a big egg on his head from the force of it.”
“We thought it was going to explode when it landed, so everyone was in a bit of a panic trying to get away from it.”
The man said another woman got a burn to her arm. “It was pretty loose.”
Another woman said she had “broken a small bone in her hand” putting her arm up to protect her 5-year-old child.
It was suggested a larger exclusion zone would buffer the crowd from debris.
The sold-out event was attended by between 6000-7000 people with 1000 people turned away at the gate.
“There was nowhere to move to. People were sitting shoulder to shoulder,” one said.
Robertson said the main issue was finding private grounds large enough to accommodate.
“You can’t let fireworks off in a public place - that is one of the problems Auckland has so you’ll end up with no fireworks display.”
He was following up with the private medical team to see exactly how many people were treated.
