Missing helicopter defies searchers' best efforts

Searchers are running out of places to look for missing helicopter pilot, multimillionaire Michael Erceg, and his Dutch passenger, Guus Klatte.

The two men have been missing since Friday and with no indication of where they could be the search for them is likely to wind down today or tomorrow.

Rescue Co-Ordination Centre staff last night planned to review the case, looking through all credible sightings and searched areas to see if there was anything else that could be done.

Mr Erceg, who is listed as the country's ninth richest man, and Mr Klatte were last seen flying out of Ardmore Airport, south of Auckland shortly before 10am on Friday.

Thirty minutes later Mr Erceg's maroon-coloured Eurocopter disappeared from the radar.

It is not known if the helicopter crashed as it disappeared from the radar or if it flew on for some time and landed elsewhere in the country.

When the men were first reported missing the search focused on the area near Raglan where people had reported hearing the helicopter.

As the week has progressed the search has headed south towards Wanganui, where Mr Erceg - a pilot for about two years - had planned to refuel.

On Monday 20 helicopters were up in the air but by yesterday that was down to six as searchers covered a more defined area.

That area was east of Mokau and south towards Wanganui where residents had reported seeing the helicopter at about 11am on Friday.

The search, like all others, was fruitless.

Maritime NZ director Russell Kilvington, who is responsible for the rescue centre, said the search had been very difficult due to rugged terrain, poor weather, the size of the area and the limited information about the route the helicopter took.

More than 20,000sq km have been searched and helicopter pilots have put in around 300 flying hours collectively.

Helicopters cost around $1500 an hour which would put the search - described as one of the biggest of its kind - at close to $500,000 for the aircraft alone.

Mr Kilvington said money was not a consideration in whether the search continued but staff had to assess what else could be done.

Last night three helicopters were flying back towards Hamilton with their radios set on a frequency that could pick up a locator beacon - although no signals had been received all week.

Following that and the review of the entire search a decision would be made as to how to progress today, if at all.

Why they can't find the helicopter

* The emergency locator beacon did not activate.

* There is no known crash point. Searchers have covered 20,000sq km in the North Island.

* Terrain is rugged and almost impossible to cover by foot unless a crash point is found.

* The wreckage is probably not visible from the air as it may have crashed through foliage and be covered.

* The helicopter is dark coloured and won't stand out from surroundings.