An off-duty NSW policeman has been killed in a 20-metre avalanche while climbing down a glacier on Mount Cook in New Zealand’s South Island.

Nathan Deutschbein, 40, was buried after he and a companion are thought to have triggered a small avalanche while climbing down the Eugenie Glacier at Mount Cook National Park at 1.30pm on Thursday.

New Zealand Inspector Dave Gaskin told local media a second man suffered minor injuries and was unable to help his friend in time. A third hiker had stayed behind in a hut and did not go on the hike.

Inspector Gaskin described the hikers as “reasonably proficient and experienced”.

The hiking pair had turned back due to poor weather when the 20-metre wave travelled 300 metres and pushed them into a crevasse.

He was later winched out by helicopter after setting off a locator beacon.

He and the injured hiker were later flown off the mountain.

NSW Police said he was an off-duty leading senior constable with the Blue Mountains Police Area Command.

“NSW Police have offered support and condolences to the officers wife and family,” a spokesperson said.

An advisory on Thursday morning warned of a moderate avalanche risk above 1200m, due to unstable snow and poor weather in the days prior, a Mountain Safety Council spokesman said.

“[It’s] an inherently dangerous place to go,” he told AAP.

An update later in the afternoon warned there was considerable risk from dangerous avalanche conditions in the area and said “cautious route-finding and conservative decision-making” were essential.

Rain had aggravated the risks in an already unforgiving environment, the Department of Conservation said.

“The snow at Eugenie Glacier was loose and slushy as warmer temperatures meant the snow hadn’t frozen for several nights,” said the department’s Mount Cook operations manager, Brent Swanson.

The death has been referred to a coroner.

Thursday’s event was the second deadly avalanche at the national park in recent weeks.

Last month, on nearby Mount Hicks, New Zealand adventurer Jo Morgan managed to dig her way out of the snow that killed her two companions, Martin Hess and Wolfgang Maier.

-with AAP