If the men have perished, the death toll at Aoraki-Mount Cook National Park in the Southern Alps now stands at 238.
Around 60 bodies of dead climbers have never been found.
Mountain Safety Council avalanche and alpine safety expert Andrew Hobman said: "There are numerous souls in the park who have never been found and that is a real possibility."
He recalled working in search and rescue at Aoraki-Mt Cook National Park, and finding a plastic boot in the Tasman Glacier that was linked to a party that "disappeared up the Linda [Glacier] 30 or 40 years earlier".
In September 2009, Malaysian hiker Kok Liang Wong, 32, went missing on Aoraki-Mt Cook and was never found. Four years later, a coroner ruled he had died by "misadventure".
Although small when compared with global behemoths like Mt Everest - which is almost 2.5 times its height - Aoraki-Mt Cook is a technically challenging mountain.
Its height and level of glaciation attract climbers from all over the world. But its difficulty is often underestimated.
The climb involves sustained glacier travel, with rock and ice climbing, and a 15- to 20-hour summit day.
The level of difficulty can change dramatically depending on weather, snow and ice conditions.
"International visitors are surprised by its scope, sheer size of it, the glacier, the terrain," Mr Hobman said.
He has reached its summit five times and attempted it "numerous more times".
Hazards include crevasses that can "easily swallow a vehicle", ice and rock falls, avalanches, as well as high precipitation levels and short weather cycles. "Things can change really quickly," Mr Hobman said.
"It's a big mountain and when you turn up there, you've got to be prepared to wait out weather and snow pack conditions, then go when you've got an opportunity.
"Being willing to say no is pretty difficult, especially if you are committed to something, travelled some distance, and planned it for some while. Your natural instinct is to forge on."
The climbing season runs from November to February. Hardly a season goes by without at least one fatality.
In 2001, a study calculated the fatality rate in the Aoraki-Mt Cook park was 1.87 deaths for every 1000 days spent climbing.
Mt Taranaki is New Zealand's second-deadliest peak, with 82 deaths.
Five people died last year in Aoraki-Mt Cook National Park, the largest number since 2008, when six perished in separate accidents.
Stu Haslett, 28, a member of the Aoraki Alpine Rescue Team and an experienced mountaineer, was its last confirmed casualty after falling on December 13.
The suspected deaths this week would be the most fatalities since March 2005, when Englishman John Lowndes, 59, slipped and pulled down his roped partner Japanese climber Kazuhiro Kotani, 29, and Kiwi guide Erica Beuzenberg, 41.
"It's an amazing mountain, in a beautiful setting, with numerous routes, and often you might have the place to yourself," Mr Hobman said.
"It's a dream situation in many ways, but it's also extremely challenging.
"You've got to know what you are doing, but even then you can get unlucky."
Our deadliest mountain
• Aoraki-Mt Cook is the highest mountain in New Zealand at 3724m.
• Aoraki-Mt Cook National Park has 19 peaks higher than 3000m and five major glaciers. Permanent snow and glacier ice make up more than a third of the area of the park.
• The first European known to see Aoraki-Mt Cook was Abel Tasman on December 13, 1642.
• It was named Mt Cook in 1851 by Captain John Lort Stokes to honour Captain James Cook, who first surveyed and circumnavigated the islands of New Zealand in 1770.
• Following the settlement between Ngai Tahu and the Crown in 1998, the name of the mountain was officially changed to Aoraki-Mt Cook.
• In Maori legend, Aoraki is their most sacred ancestor and represents a link between the natural and spiritual worlds.
• The first recorded European attempt on the summit was made by Irishman the Rev William S. Green, Swiss hotelier Emil Boss and Swiss mountain guide Ulrich Kaufmann on March 2, 1882. It's believed they got to within 50m of the summit.
• The first known successful ascent was on Christmas Day 1894 by New Zealanders Tom Fyfe, Jack Clarke and George Graham.
