Police confirmed that the Anzac Day crash happened about 6.45am. The wreckage was found on a farm, off Paekakariki Hill Rd and near Pukerua Bay, north of Wellington.
Four people were onboard. A Wellington Free Ambulance spokeswoman said three people were dead, and a fourth was taken to Wellingon Hospital in a serious to critical condition.
The Defence Force confirmed the RNZAF iroqouis was one of three from Ohakea Air Base going to Wellington for a Anzac Day service.
Several emergency services - including the Westpac rescue helicopter - are involved.
A HeliPro pilot, Ned Lee, who had flown over the crash scene said he was surprised anyone had survived.
He said the helicopter was upside down on the hillside.
Defence Force communications director Commander Phil Bradshaw said in a statement there would be no official comment until the force had established what happened.
Pukerua Bay resident Kathy McLauchlan said she could see the crash site from her window.
Weather conditions at the time of the crash were "extremely misty", she said.
"Since the mist has lifted we can see it."
Military and rescue helicopters were circling the area.
The crash happened quite high on the hills overlooking Pukerua Bay, Ms McLauchlan said.
Military and rescue helicopters were circling the area and had been using the beach adjacent to the hills and State Highway 1 to transport the injured to an ambulance.
