A colossal rockfall came only a few hundred metres from engulfing a popular climbers' hut in the Aoraki Mt Cook National Park.
Twelve people were in the hut as huge quantities of rocks, which climbers described as sounding like a Boeing 747 coming through, plunged hundreds of metres down Mt Dixon about 2.15pm yesterday, shooting plumes of dust high into the air.
No-one was injured, including other climbers who were further up Mt Dixon when the rockslide happened.
Climber Andrew McGregor, who was in the Plateau Hut, said the rocks came to a halt about 200 metres away.
But the Sydney student said he and the other climbers were not afraid.
"Those there didn't think they were in any immediate danger. Everyone treated it as an amazing piece of mother nature.
"It was quite awe-inspiring," he said.
McGregor described the avalanche as a "powerful wave" tumbling down the mountain, making a "rumbling and thunderous" noise in the process.
Others, who were closer to the rockfall on Mt Dixon, said it sounded like a "747 [plane] coming through", McGregor said.
Once the avalanche had settled, it was about 3km by 500m in size, he said.
"It was quite a significant avalanche."
McGregor, who was in the country for a week and would return home on Wednesday, said he was not put off climbing by the natural disaster.
"At the end of the day it's not something that happens that frequently. I don't think it's going to happen again anytime soon."
McGregor spent last night at the Unwin Hut near Mt Cook.
Department of Conservation spokeswoman Shirley Slatter said there were 12 climbers, including guides, in the hut at the time and a guide she had spoken to was "pretty amazed" by what was happening around them.
A party of three which was on Mt Dixon when the rockfall occurred, made its way back to the hut late in the afternoon.
Another party of three was continuing a climb up Mt Cook itself.
"They will have a wee surprise when they come down tomorrow as they will actually have to cross the debris to get to the hut," she said of the group.
Helicopter company Heliworks put on a flight for DOC staff to fly up and check the slide and the nearby hut yesterday.
The decision was made to close the hut as debris came to rest within 150 to 200 metres of it. The climbers were flown out from the hut last night, with some choosing to be flown to other huts in the park to continue climbing.
"There is the potential for more to come off, Slatter said.
She said it was the largest rockslide in the park since the top 10 metres fell off Mt Cook in 1991.
Rob Randell from scenic flight operator Helicopter Line saw the rockfall from the air and "couldn't believe the scale of it".
"It's like a huge avalanche but it's a dirty, rocky, icy avalanche.
"It really is massive."
"It was a "blessing" nobody was injured.
Senior engineering geologist for GNS Science Graham Hancox described the incident as a "landscape-changing event".
"This is a major avalanche and there'll be more than a million litres of debris. It was an extremely rare event and it's taken quite a substantial notch out of the south face."
He said the hut was "naturally protected" by an ice plateau and said the slide would "have been enormous to come anywhere near the hut".
- © Fairfax NZ News