The wife of a 69-year-old Auckland man looked on in horror as he slid down a bank and over a cliff while tramping the Milford Track.
George (Clyde) Little was killed while walking on a steep section of the track near Mackinnon Pass, the highest point on the Milford Track, about 11.30am on Friday.
Mr Little and his wife, Jill, were part of a 32-member Rotary tramping group staying at Department of Conservation huts in Fiordland National Park. The group included New Zealanders and Australians, and one of the leaders was Otago Regional Council chairman Stephen Woodhead.
He said Mr Little was walking near the back of the group, with his wife and two of the group's other leaders acting as "tail-end Charlies" to ensure no one was left behind.
"The track is in good condition at that point. We know he was walking single file with his wife behind him.
"He slipped down a sloping rock face and then there was a drop-off.
"She saw him pop over and he disappeared quickly. It must have been horrifying for her."
The drop was estimated to have been between 100m and 150m.
Mr Woodhead did not believe weather or track quality were factors in the accident. "We don't know whether he tripped or whether he had a medical event. It's just a complete and utter shock to the group."
The cause would have to be determined by the coroner, he said.
A rescue helicopter flew Mrs Little and Mr Little's body to Te Anau.
Tour organiser Peter Vollweiler, said he had arranged tours for 30 years and about 17,000 people had walked the track without any fatalities.