The cold weather which caught four hikers off guard on the Tongariro Alpine Crossing, leading to the death of one, had been forecast the day before the fateful trip, a police spokesperson said.
The four set off to do the Tongariro Alpine Crossing on Monday wearing only hoodies, sweat pants and running shoes.
One of the party was later found dead. Police named the man as Sateesh Babu Halehally-Chikkanna of Bangalore, India.
"Considering what we know, it would appear that he has died from exposure to the cold," Senior Constable Barry Shepherd of Taupo Police said.
"When you go into that alpine environment when there's serious weather, dressed like they were dressed, you're going to die from the cold."
Although the men also had beanies and gloves, they were useless when wet and weather conditions on Mt Tongariro on Monday were poor, he said.
Shepherd said the cold weather which struck the mountain on Monday afternoon had been forecast by at least the day before.
He said there were many unanswered questions, including why three of the group, two aged in their 20s and the other man in his 50s, had left their 53-year-old companion behind, and why they had started at the Ketetahi end of the crossing, which requires a much longer climb to the summit than the usual starting point at the Mangatepopo Valley.
After splitting up at the bush edge above Ketetahi carpark, the group of three had continued on to Emerald Lakes but the weather was so bad there that they abandoned their original plan to hike to Mangatepopo and instead turned off and headed down the mountain to Oturere Hut. From there, they rang police saying they were cold and wet.
Shepherd said the group were told they had two options: Stay in the hut or walk out to the Desert Rd. They walked to Waihohonu Hut, near the Desert Rd, where they were met by a Turangi Land Search and Rescue group and taken back to Ketetahi carpark. It was then that Halehally-Chikkanna's wife alerted police that her husband had not arrived.
"The facts showed that he's continued on up over the crossing and over the top."
Halehally-Chikkanna's body was discovered late yesterday morning on the descent between Red Crater and South Crater on Mt Tongariro. Conditions on the mountain were still so bad yesterday that the searchers were cold and being blown off their feet.
Shepherd said it was a tragic outcome and very, very sad.
The death has prompted Mountain Safety Council chief executive Mike Daisley to warn anyone considering tramping in the region to properly prepare for alpine conditions.
"The word 'Alpine' was added a few years back to what we know as the 'Tongariro Alpine Crossing' for a reason.
"Many people may not know there is still deep snow on the ground in many places as well as potential avalanche paths in this region," Daisley said.
It was too soon to know how the incident happened, but sticking together as a group is the recommended policy, he said.
"We're working with police and with the coroner's office in due course to ascertain exactly how and why this group got separated.
"People who get separated from their group make up a mere 5 per cent of the total tramping fatalities in the last 10 years. Hypothermia contributed 6 of the 57 fatalities during that period," Daisley said.
The tragic death appeared to be preventable and should be a stark reminder to people explore the alpine regions of New Zealand that when things go wrong in that kind of environment "the consequences are often very high".
"If this had happened at lower altitude there would have been a higher chance of surviving this 'unexpected night out'. Sadly, his family and friends are now grieving," he said.
Senior Constable Barry Shepherd said police had four key messages for anybody thinking of doing the Tongariro Alpine Crossing:
1. Wear appropriate clothing.
2. Keep an eye on the weather.
3. Stick together.
4. Be prepared to turn back.
Before yesterday's fatality, the last person to die of hypothermia on the Tongariro Alpine Crossing was American tourist Raydene Shepard, 70, in 2006.
A recent study by the Mountain Safety Council showed the Central North Island was disproportionately represented when it came to search and rescue missions across New Zealand.
A Walk in the Park?, which was released in July, analysed tramping trips, fatalities and injuries during those trips, and search and rescue missions.
The report's data showrf 14 per cent of all New Zealand's search and rescue incidents for trampers were in the Tongariro National Park, and 22 per cent of all New Zealand's Saturday search and rescue callouts were to the park.
The report stated that in 2016/17 there were 141,000 walkers on the Tongariro Alpine Crossing and numbers were continuing to rise.