They were killed in the crash and a fourth crew member is in hospital in a critical condition.
Authorities are now trying to work out exactly how the helicopter crashed.
The Iroquois helicopter was one of three on its way from the Ohakea air base to Wellington to take part in fly overs as part of Anzac Day services.
The crash happened just before 6:30am.
The helicopter was flying in heavy fog and crashed into the Paekakariki hill, 40 kilometres north of the capital.
Pictures show the helicopter upside down and in a number of pieces on the hillside.
Officials from the Royal New Zealand Air Force are at the scene and will hold a press conference later today.
Details about who was on board have not been released.
The New Zealand Government has ordered a full inquiry into the crash.
Defence minister Wayne Mapp says the fleet was due to be replaced next year, but it is not known if the age or maintenance of them had anything to do with the crash.
"They are being replaced with two types of aircraft. The first of those will be delivered actually at the end of the year or beginning of next year," he said.
The government says this is a sombre reminder of the dangers its military personnel face.
Since 1966 there have been 4 other crashes in the fleet of 14 Iroquois.