Searchers in rugged mountain country near Nelson were setting out at first light today to continue looking for Palmerston North tramper Alistair Levy, who has been missing since Sunday.
They battled rain and rough terrain near Mt Owen in the third day of the search yesterday.
Search co-ordinator Sergeant Mike Fitzsimons said police held grave concerns for Mr Levy's welfare given the time that had elapsed since he was last heard from.
A further aerial search was planned for today.
Police found Mr Levy's bike on Boxing Day and said a text message sent by the 54-year-old teacher from the mountain's summit in Kahurangi National Park was the last contact made by him.
Four search teams looking for Mr Levy camped in the Mt Owen area.
They were joined by three new teams yesterday, including a second search and rescue dog.
Mr Fitzsimons said the search started on Christmas Day when Mr Levy did not join his wife and other family in Christchurch for Christmas.
His bike was found at a cafe where he had arranged to leave it with the owners.
Cafe co-owner Graeme Crook said he could not remember when Mr Levy dropped off the bike, only that he had been one morning recently.
Mr Crook contacted police on Boxing Day to tell them the bike was at the cafe.
"We were really busy when he came in.
"A lot of people leave bikes and cars here.
"Sometimes I have eight, nine or 10 cars."
Mr Levy was believed to be carrying a purple-and-black backpack, but did not have an emergency locator beacon with him.
Mr Fitzsimons said: "It's a big mountain, and it goes from being awesome to scary, depending on where you are."
He said searchers still thought Mr Levy had walked over the top of the mountain and had planned to come back via the cafe.
The discovery of his bicycle confirmed that view.
Graham Levy, the missing man's brother, said Alistair had been tramping for 30 years, and did not always take an emergency beacon.
He had been progressively tramping through the entire South Island.
The Mt Owen trip was to fill in a gap.
Helicopter pilot Tim Douglas-Clifford, who used night-vision goggles in the search, described the area as extreme, hostile terrain and said the search was challenging.
"Going out on the south side it's very steep, with a lot of caves, big craters, jagged rocks and deep crevasses," he said.
"It drops down into heavy bush, and it's almost impossible to see through."
It was an area where part of the first Lord of the Rings movie was filmed.
A local caving expert, Nelson Speleological Group president Andrew Smith, said people travelling on the south side of Mt Owen "absolutely" needed their wits about them.
Smith said the group had been asked to help with the search, and a caver was on the mountain advising the police.
"It's not too bad a country to find your way through if you know where you're going, but if you don't, it's tough," he said.
Smith said the area was one of only two places in the world with glaciated marble, and this made it attractive to trampers.
"The Lord of the Rings [producers] knew what they were doing when they took their movies up there," he said. "It's not like another area in New Zealand. It's not just a normal tramping area."
The terrain included marbled slats and lots of holes, from 1 metre in diameter to much larger.
"Some go down only a few metres, but some go down quite a bit more."
There were also sharp edges in some areas, which was quite concerning, he said.
"Even just a simple fall could injure him quite easily."
He said route-finding was also extremely difficult, and it was quite easy to get lost, even in such a small area.
- Manawatu Standard
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