Wanaka Land Search and Rescue volunteers found and positively identified Ms Yun's pack in a treacherous gorge area of the swollen Dart River, about 300m downstream of the Dart Hut.
Wanaka police search co-ordinator Sergeant Aaron Nicholson said the find confirmed searchers' worst fears.
The pack's damaged condition "clearly indicated" it had been torn from Ms Yun by the force of water.
"This, coupled with [other search team work] confirms our earliest fears that Ms Yun has been caught trying to cross one of the side creeks that bisect the [Cascade] track."
Police and LandSAR staff regretted the "tragic and avoidable loss of life", he said.
The gorge area in which the pack was found is a jumble of massive rocks and white water.
"There is every chance the body is buried under silt or trapped well below the surface."
Ms Yun's former husband, Oleg Amiton, flew to the area yesterday morning with one of her friends and an alpine guide from Wanaka's Aspiring Guides to conduct a private search.
The pair are originally from Kazakhstan and have a 4-year-old daughter, Liann, who was born in New Zealand.
Ms Yun and Mr Amiton married in Auckland about five years ago.
Aspiring Guides director Jean Clairmonte said the group was expected to make its way back to Aspiring Hut, in the West Matukituki Valley, by about 8pm.
She was uncertain where the private searchers had looked. She was unsure whether they intended to return to Wanaka or keep looking today.
Mr Amiton had been informed by radio about the find of his former wife's pack, she said.
Ms Yun went missing on New Year's Eve while attempting to tramp the mountainous Cascade Saddle (1524m) track from Mt Aspiring Hut in the West Matukituki Valley to the Dart hut.
She was last seen at 9.30am heading up the Cascade track.
She had ignored advice from the Mt Aspiring hut Doc ranger not to attempt the route because of bad weather.
Sgt Nicholson said forecast bad weather could further stifle hopes of a successful search to locate Ms Yun.
"Weather permitting", the group would return today and make a final search attempt focusing on the area immediately above and below where the pack was found.
Specialist swift-water teams would enter the river and sniffer dogs would also be used.
"Realistically, our chances are slim," he said.
On the day Ms Yun went missing, the Dart River was running at 10 times above its usual average flow levels.
Bad weather has hampered searchers' efforts, with sleet, high winds, torrential rain, and snow experienced during the past week.
Ms Yun's pack was found during a low-level helicopter search of the river gorges.
