Five people survived the sinking of their vessel near Cape Colville at the top of the Coromandel Peninsula on Saturday, but police say it could easily have been a tragedy.
A may day call was issued at 5.45am when the vessel began taking on water.
Two of the five occupants had to be winched by helicopter from the vessel to HMNZS Canterbury. The other three were removed by Coastguard personnel.
Police say the boat completely vanished from the surface of the sea as the last of the five was taken off.
Inspector Lou Alofa says members of the group had early stage hypothermia and were being taken to Auckland hospital for assessment.
The cause of the sinking is unknown.