Erceg helicopter search fleet now at 20

Three more helicopters have joined the search for missing multi-millionaire Michael Erceg and a Dutch passenger who disappeared on a flight from Auckland to Queenstown on Friday.

Search officials added three more helicopters to the fleet about mid-morning and 20 machines were now searching between Mokau on the west coast north of Taranaki, and Wanganui.

Mr Erceg's Eurocopter was last seen near Mokau in north Taranaki on Friday as it headed to Wanganui to refuel.

Rescue Co-ordination Centre spokesman Steve Corbett said the search area was mostly covered by thick bush and it would be extremely difficult to find a downed helicopter.

However, he said searchers believed there was good chance Mr Erceg and his passenger, beer company executive Guus Klatte, were still alive.

"We have got to presume that. That is the only way you can do it."

Each helicopter would cost about $1500 an hour to keep in the air but Mr Corbett said he was impressed by the way the aviation industry had responded to the search.

He said with 20 helicopters in the air, there was also the risk of a mid-air collision.

The search area had been split in two, one south of Mokai to Pohokura east of Inglewood, and the second between Stratford and Wanganui.

"It is pretty rough country but fortunately, with the conditions they are working in and the challenge they face, that is why it is so helpful to have such a huge amount of skill and experience in the majority of pilots.

"It is a massive task," Mr Corbett said.

He said the weather was "not great" with drizzle and low cloud and it was forecast to get worse.

- NZPA