Police said they were called to The 309 Road just after 2pm today where two people were found with gunshot wounds.
One person was arrested and charges were being considered, police said. They were not seeking anyone else.
A former army medic who gave CPR to one of the victims confirmed that the men involved were pig hunters.
The man, who asked not to be named, told RNZ's Checkpoint programme one man died and one man was airlifted to hospital with gunshot wounds.
He said 120 children were also onsite celebrating the end of the school year.
"I was serving customers in my little business here when someone came running in and said they heard gun shots ... grabbed my first aid kit and took off."
He said he found an injured man near the edge of his property and put him in the recovery position and got a compression bandage for what looked like a gunshot wound before starting CPR.
"Another resident (turned up) and between us we both did CPR for 20 minutes until the Westpac helicopter arrived and pronounced him dead, and that's when we stopped stopped doing CPR....
"Whilst I was giving CPR, the local policeman arrived, offered a more extensive first aid kit than I had, and then shortly after there was an abundance of police, the local fire service, St John's, and very quickly two Westpac rescue helicopters."
There was a second man, who appeared to be a "young lad" in his 20s, the man told Checkpoint, who had a gunshot wound to the upper chest.
After he "exited the situation" he saw the young man "on a gurney being treated by the Westpac service personnel".
He said it was pretty clear the pair had been hunting as there was a dead pig nearby.
While there had been children on-site, the man said he did not think they would have see anything as they left through a different exit on the property.
Westpac rescue helicopter told RNZ that crew were transporting a patient to Auckland City Hospital following a shooting incident.
A St John spokesperson confirmed one person had been flown to hospital in a serious condition.
The spokesperson said they were notified just before 2pm and one ambulance, one first responders unit and two helicopters attended.
Police said The 309 Road is closed and people were advised to avoid the area.
