It was unclear if the man was alive when pulled from the lake.
Climber Hazel Phillips was at the scene shortly after the accident and said she "partially witnessed the retrieval".
"Conditions were windy and icy underfoot near and this presents a sliding risk," she said.
"We also witnessed someone fall while descending Dome [a peak on Mt Ruapehu], lose his ice axe and thankfully come to a stop on a flat part of the Whakapapa Col.
"He was badly equipped and not experienced — he is lucky he did not end up in the crater lake, too.
"With spring conditions softening the snow above the lifts on Ruapehu, this is a high risk time as people who aren't used to serious alpine conditions begin to venture into unpatrolled and uncontrolled terrain.
"This is an incredibly sad outcome and a timely reminder for all backcountry snow users to ensure their skills are nailed and their gear is on point."
Another comment said a patroller had to go into the lake to help retrieve the man, who was already dead.
Reports from the scene were that a group of climbers slipped near the "Pyramid" traverse of Mount Ruapehu, which is the high point of a circumnavigation around the crater lake.
Herald reporter Martin Johnston was up at Crater Lake skiing around 1.30pm today, just before the accident reportedly occurred.
He said he suspected the man was part of a group of six climbers who he passed on his way down.
Johnston thought the group came up from Whakapapa ski field and climbed over a little Dome peak.
"They would have walked off an icy face so they probably had crampons," Johnston said.
"Three of them went down near the edge of crater lake — it was very cold up there and conditions were firm and icy."
Chief executive of Ruapehu Alpine Lifts, Ross Copland, said some of his workers had assisted with the operation.
"Our company is the founding company of the Ruapehu Alpine Rescue Organisation, so our senior patrollers were picked up by their helicopter to assist with the search."
RAL staffers had also helped retrieve the body, as well as taking the man's two companions to the Whakapapa care clinic to be checked over.
Copland said the incident would not halt any lift operations or result in closures as it happened outside of the skiing area. It could, however, cause closures around the crater lake itself.
Ruapehu iwi Uenuku, Ngāti Tūwharetoa and Ngāti Rangi announced a rāhui, or temporary access ban over the area yesterday morning, lasting till sunrise on Wednesday.
To show respect, all climbers, trampers and skiers are asked not to go above the boundaries of the ski areas at Whakapapa, Tūroa and Tukino, or above a line 2300-metre above sea level on the mountain.
The rāhui is supported by the Department of Conservation and Ruapehu Alpine Lifts.
In October 2017, New Zealand climber Richard Ebbett died after also falling into the crater lake.
Police said at the time it appeared the 30-year-old adventurer had slipped and fallen. Ebbett had also saved a young girl from drowning in 2001.
