The three climbers missing on Aoraki-Mt Cook since Monday are feared dead, police have said this morning.

A search resumed at first light this morning with three helicopters taking to the skies.

However, there has been no sign of overdue climbers Dr Michael Bishop, 53, from Sydney, and Raphael Viellehner, 58, and his son Johann Viellehner, 27, from Germany.

"The situation is grim," a police statement says.

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"It was hoped that if they had survived the storm they would have been spotted from the air today.

"It is still unknown what has occurred to the men but it is believed that they have perished on the mountain.

"The family have been informed of the news."

The search will now be reevaluated, police say.

A further 30 cm of snow has fallen at Plateau Hut with larger amounts settling higher up the mountain.

Further aerial searchers will take place over the next few days in attempt to locate their bodies, police said.

The Christchurch ACR team have returned home and the DOC rescue team are back on standby at Mt Cook village.

Last night, Dr Bishop's friends and family gathered to pray for the three missing men.

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Dr Bishop, 53, started climbing as a medical student some 30 years ago. On two previous trips to New Zealand, he'd had to turn back from Mt Cook-Aoraki after nearing the summit, his son Joshua Bishop said.

"Cook's something he's really wanted to do. On Christmas Day, he was like: This is it. We've got a good period of weather coming up and this will be the time to do it."

Dr Bishop hadn't planned to climb with the Viellehners but after meeting them they had decided to summit together. Joshua believed the three met at Plateau Hut.

Joshua was confident his dad was prepared but said an injury among any of the three could complicate efforts to find shelter.

"He's very safe. He's very wise when it comes to climbing. He goes out there with the right gear. He doesn't go unprepared.

"One time he got caught in a big snowstorm and he had to make an igloo, or a snow cave, and he did it and survived and came back with all his limbs and fingers...so he did the right job."

Joshua said it was good the three men were together, combining different kinds of expertise. He believed Johann Viellehner, 58, had climbing experience in cold parts of Russia. Raphael Viellehner was 27, the same age as Joshua.

"I have complete confidence the three of them would have put their heads together and said: Let's find a cave, let's make something to stay warm."

Joshua said the efforts of authorities and volunteers in New Zealand were heartening. "It's been really encouraging to see there are so many people there who care about dad as much as I do."