A 'devastated' Sir Tim Wallis was this afternoon heading to the spot on Lake Wanaka where his son is believed to have died in a helicopter crash.

This comes as the Royal New Zealand Navy has been called in to help with the recovery of Matthew Wallis, which was believed to be 47m below the surface of Lake Wanaka.

George Wallis told the Otago Daily Times from Hawaii his brother Sir Tim was "absolutely devastated".

He said Sir Tim was this afternoon making his way out to Stevensons Arm, where police believed they had discovered the wreckage of the helicopter belonging to his son. George described Matt as "very energetic" and his loss would leave a "big void".

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The 39-year-old was the only person on board a helicopter that crashed in Lake Wanaka on Saturday afternoon.

The Police National Dive Squad arrived in Wanaka yesterday and have found what they believe to be the wreckage about 47 metres below the surface of the lake.

"We have asked for the Navy's expertise and specialist equipment, which can operate in deeper waters.

"A team of Navy underwater search specialists is due to arrive in the area later this afternoon to liaise with Police and make an assessment of the scene," a spokesperson said.

Matthew's brother Jonathan Wallis Lake Wanaka said he remained determined to bring him home to his 5-year-old son Arthur and wife Alice.

"He's a wonderful father to his son Arthur and a very good husband, if not a little challenging at times too, to his wife Alice."

Jonathan Wallis spoke to the New Zealand Herald just moments before heading out for day three of the search.

"At this stage the thoughts really haven't gone to remembering him, the focus is on finding him."

He said his 39-year-old brother was one of kind who had affected a lot of lives.

"He had a very wide circle of friends and colleagues. He was a good mix of his mother and his father and is very good at what he does."

In a Facebook tribute Jonathan Wallis said: "I miss you already and will never ever forget you", and promised the family would take care of his wife and son.

Detective Sergeant Derek Shaw said the area was under a severe weather watch on Saturday and police no longer expect to find Wallis alive.

"We have now transited into a recovery phase and we do not believe that the pilot is still alive," he said yesterday.

Police, LandSAR, Coastguard boats and police divers have been searching for Wallis since he went missing.

It is anticipated that the operation will be run from a large barge on the water positioned in Stevensons Arm, near where debris was originally found.