A diving and salvage company says retrieving the wreckage of a plane lying deep underwater off the Waikato coast would have to be done within minutes because of the danger to divers.
The bodies of 2degrees chief executive Eric Hertz and wife Kathy are thought to be inside the aircraft which is lying upside down at a depth of 56 metres.
The couple were flying from Ardmore near Auckland to Timaru when they reported engine problems on the twin-engine plane which disappeared off the radar off Kawhia, near Raglan, about midday on Saturday.
Deteriorating weather conditions on Wednesday prevented search teams from further examining the wreck, with Waikato police says the bad weather is likely to continue on Thursday.
New Zealand Dive and Salvage says the operation would require experienced deep sea divers who would need to act very quickly so they do not run out of air or suffer the dangerous condition nitrogen narcosis.
The firm says there is a risk the plane could fall apart as efforts are made to bring it to the surface.
A Navy dive support vessel is on its way from the Devonport naval base in Auckland to help retrieve the plane.
The Manawanui commanding officer, Lieutenant-Commander Kerry Driver, says the vessel is bringing equipment such as a crane and a recompression chamber.
"We're really there just to support the New Zealand police. They've requested our support due to our capabilities. We just provide advice and equipment for them to conduct their search and help them to hopefully provide some closure to the families."
It is due to arrive at the crash site on Friday.
Meanwhile, the Civil Aviation Authority says it is gathering information and data to establish what went wrong during the fatal flight.
In a statement, the families of Mr and Mrs Hertz have thanked the New Zealand community and authorities for their support and efforts.