Mr Regner and his companions caught up with him about 20 minutes later taking another rest, and decided to accompany him the rest of the way.
They said he was not in good condition, was wearing unsuitable shoes and only had a light rain jacket. Four hours later, after covering only 4km - with several kilometres to go - they became concerned they would not make it out in daylight.
Sara Sleiman, 25, said despite asking the man at regular intervals if he was all right, he said he was fine. Mr Regner a group of Argentinian tourists stopped to help but no-one realised how bad the man was until it was too late. The shuttle driver also tramped several kilometres up to the group and did what she could, but the man died in Mr Regner's arms before medical assistance arrived.
"I just realised he had died. It was just crazy," the distressed tourist said.
The four visitors, helped by Turangi Victim Support, say they wished they had done more and ignored the man's refusal of help. They also want to emphasise how important it is for people doing the Tongariro Alpine Crossing to know their limits and ensure they are fit enough and properly equipped for the environment.
The group started the seven-hour crossing in fine, sunny weather but conditions had changed by late afternoon and although it was not cold it was raining with low cloud. Ms Sleiman said one man she saw at the 10km mark was in bare feet.
Although there were information signs about fitness, they might need to be larger and accompanied by some statistics illustrating that people had died on the Crossing," she said.
"A little more fear might help people calculate the situation better."
Turangi Police officer in charge Sergeant Te Reipa Morunga says the young people did a fantastic job by staying with the man. The shuttle bus driver had also done all she could. The death has been referred to the coroner.
Detective Sergeant John Wilson of the Rotorua CIB, who also leads the Rotorua police search and rescue squad, said we should always be prepared before embarking on things like the Tongariro Alpine Crossing.
"Being prepared physically and prepared equipment wise is important, but it may be that in this case it might not have changed the outcome."
Mr Wilson said it was very important to plan your trip and there were several things you could do to make it easier for yourself, as well as rescuers if it came to that.
"Seek out local knowledge, plan where you're going and allow a reasonable amount of time. Let somebody know your plans and that they need to raise an alarm if you haven't returned when you should.
"Check the forecast and be prepared for weather changes. Know your limits, don't go doing anything that you're not capable of. Take sufficient supplies and appropriate means of communication.
"It might not guarantee that nothing bad will happen, but sorting these things puts you, and rescuers, in the best position," Mr Wilson said.
Additional reporting by Kyra Dawson
