Adventurer Jo Morgan, wife of businessman and philanthropist Gareth Morgan, has miraculously survived after being buried beneath a major avalanche for 30 minutes before digging herself out of the snow.

Two guides are confirmed dead after the avalanche on the South Island's Mt Hicks and into the Harper Saddle area near Mt Cook/Aoraki at around 5.30am.

"I'm lucky to be alive," Morgan told Newshub.

She described her heartbreak to 1 News about the moment she realised her two "dear friends" had died.

"I'm absolutely broken," she told 1 News.

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"We weren't being foolish or anything and we just hit a slope that ... it was laden with the type of snow that avalanches [happen].

"We all got thrown down the hill tied together.

"They were buried and I was buried too, but I had my face out so I could continue to breathe."

Area Commander Inspector Dave Gaskin confirmed both victims were male guides, aged in their 50s.

They have not yet been formally named, he said, as while they are both New Zealand residents, they are from overseas and their families need to be contacted.

Gaskin understood that both men were originally from Germany.

The trio headed off at 2am this morning for the top of Mt Hicks, which they reached.

But on the way down on the southwest ridge, an avalanche engulfed them.

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Rescuers arriving on the scene performed CPR on both guides. But Gaskin believes one of them may have been killed almost instantly.

The bodies are being transported to Christchurch for autopsies, police confirmed.

It's understood that Morgan "swum through the avalanche", which Gaskin said was a "pretty standard technique" to stay close to the surface.

"When the avalanche ended, she's had one arm or both arms out of the snow and managed to get out of the snow and set off the alarm," he said.

Gaskin said it was an isolated, wilderness area but they were well-equipped and "just unlucky in the situation they found themselves in".

"They had all the gear," he said.

Avalanches are a "constant threat" in the Mt Cook/Aoraki region, Gaskin said, and even more so with the recent bad weather, which has seen new snow sitting on ice.

"Climbing mountains is an extreme sport. There is an element of risk," he said.

"These people were well-equipped, they were really experienced and knew what they could do to minimise risk, and they've done so, but on this occasion the mountain has beaten them."

He understood that Morgan was uninjured but will be affected by being involved in such a "terrible tragedy".

The small guiding community will also be dramatically affected by the loss of two lives, he said.

Morgan told Stuff it was sad time for the climbing community and thanked those who had answered her beacon to come to her aid.

Department of Conservation director-general Lou Sanson told the Herald that Morgan had "done all the right things" and having her personal locator beacon (PLB) by her side "has undoubtedly saved her life".

Morgan has been "completely buried" by snow for around half an hour, but was able to activate her PLB. About 40 minutes had passed before she had dug herself out.

"She was able to scratch around, activate her PLB, punch through the snow and dig the snow from around her head and face and get her legs out," Sanson said.

"She had her PLB right close to her body which has undoubtedly saved her life. I would have to say it's a textbook recovery of getting out of an avalanche, and it's just so sad for the other two.

"When she got to the surface, she was getting cold and couldn't see her two companions."

The three climbers were operating on one rope when the large avalanche struck.

The Rescue Coordination Centre was alerted at about 6am.

The Westpac Rescue Helicopter was scrambled from Christchurch at around 6.50am, with medical supplies and an intensive-care paramedic onboard. Pilot and crewman Wayne Ledgerwood said the flight south took around one hour.

Meanwhile, two rescue teams had reached the avalanche site by local helicopters and were working on resuscitation and on bringing the three patients off the mountainside.

Once they got brought down to the Mt Cook/Aoraki village helipad, the Christchurch crew continued resuscitation efforts.

Sanson comforted his friend at Unwin Lodge this morning after meeting the rescue helicopter off the mountain.

"She's strong but shattered," he said.

An experienced climber who says he has descended the route on which the incident happened said Morgan was fortunate the group had not been pushed off the ridge to the glaciers on either side of Harper Saddle.

Police senior constable Les Andrew confirmed a party of three people were ascending the mountain when they were caught in the avalanche.

He says the deceased are two men - both mountain guides.

Newstalk ZB is reporting the two guides were both very experienced.

Andrew said police have begun informing next of kin and the deaths will be referred to the coroner.

Sanson said Morgan was an experienced climber.

"Mt Hicks and Torres [Peak] were the last two of the 3000ft peaks that she was trying to do – she has done 22," Sanson said.

"We're just feeling shattered. The DoC staff have been so professional in how they responded this morning and really just got in there and done the job. But unfortunately it was too late to bring the other two out."

Jo Morgan's daughter Jessi wrote on Facebook: "Just an update that Jo is safe and back at Mt Cook village. Thanks for all your support and messages."

Yesterday, Jo Morgan posted on Facebook that conditions had been bleak at Empress Hut the last couple of days but said a 20-hour weather window meant they would plan to leave for Mt Hicks at 2am on Wednesday.

She posted on October 28: "Heavy packs and an overnight bivy on the way got us to the inaccessible Empress hut up the Hooker Glacier.

"Light snow has been frequent. Today is a rest day after many hours following the knee-deep steps and sticky snow that added an extra kg to your many upwards steps.

"Yes I wish I'd done more training, but have decided I excel in suffering."

Rescue teams and rescue helicopters raced to Mt Hicks this morning after receiving the locator beacon signal, a Rescue Coordination Centre New Zealand spokesman said.

Two helicopters, eight alpine cliff rescuers and an avalanche dog searched.

A helicopter with medical supplies and an intensive care paramedic was also sent from Christchurch.

Mountain Safety Council spokesman Nick Kingstone said there was a lot of snow in the mountains, with considerable avalanche danger above 1800m.

"Even on a low danger rating day, it doesn't mean there's no avalanche risk.

"It doesn't actually take a lot of material or snow to sweep a person off their feet."

Mt Hicks, 3198m, is a mountain in the Southern Alps within the Mount Cook National Park.

Gary Dickson, who has more than 30 years of climbing experience, said if the rescue was on Mt Hicks it was a mountain that was tricky and one of the more difficult mountain climbs in New Zealand.

The Alpinism and Ski owner operator said the climbing difficulty in Mt Cook Regional Park was scaled from one to six. The easiest route on Hicks was a four, while there was some that were a five.

There were several routes up the mountain, the most popular was the south face, which is a series of steep climbs.

"It's steep ice climbing for New Zealand," he said. "There is an awful lot of difficult climbs there."

Avalanche Advisory New Zealand (AANZ) has warned of rapidly changing volatile spring conditions in the Aoraki/Mount Cook National Park area.

A spokesman said a high degree of caution was advised until 10am tomorrow.

Dangerous avalanche conditions, careful snowpack evaluation, cautious route-finding and conservative decision-making was essential from above 1400m, he said.

The latest advisory at www.avalanche.net.nz says there is a considerable risk of avalanches in Arthur's Pass, Craigieburn Range, Mt Hutt and Aoraki/Mt Cook.

Avalanches can happen at this time of year as the warmer temperatures, combined with rain, increased risk.

A week ago three hunters had a lucky escape after an avalanche brought snow crashing onto their tents in Fiordland, at the head of Lake Te Anau.

The incident also follows the death of Caleb Jennings earlier this month.

The 31-year-old was seriously injured while climbing near Mt Harper, in Mid Canterbury, on October 22. He died in Christchurch Hospital three days later.

Jennings had been a member of the New Zealand Alpine Team.

More than 140 people have died in avalanches in New Zealand, according to records dating back to 1860.

One of the worst incidents happened in August 1863 when a massive avalanche buried a camp of goldminers in Otago, killing 41. In modern times avalanches most often claim the lives of climbers.

Another tragedy occurred on June 23, 1966, when a rescuer was killed in an avalanche during an unsuccessful attempt to rescue four climbers trapped on Mt Rolleston.

In 2015, Sydney skier Roger Greville died after being pulled from avalanche debris near the Devil's Staircase, near Queenstown.

Sanson is in the region today to attend a funeral of one of the DoC staff members killed in the Wanaka helicopter crash.

DoC rangers Paul Hondelink, 63, and Scott Theobald, 59, died along with pilot Nick Wallis, 38, when their chopper crashed soon after take off from Wanaka airport on October 18.

A funeral service for Theobald, who pioneered the use of pest control dogs, is being held at Glentanner Holiday Park, Aoraki/Mt Cook at 2pm today.

"All these people are known to our DoC staff, so it's another heart-wrenching blow," Sanson today told the Herald.

"My whole purpose of being here was to really focus on Scott and give him the very best send-off we possible can just 15 minutes down the road. It's a stunning day here, but such sad circumstances."