The warning followed the surprise discovery of avalanche debris up to 3m high on the usually low-risk Greenstone Track, at an altitude of only 500m above sea level.
Doc Queenstown Regional Visitor Centre supervisor Andrew Evans and two other rangers were on a training exercise last week when they encountered the "sizeable" debris blocking their path.
"The avalanche path ... is categorised as a one-in-10-year path," Mr Evans said yesterday.
"The Greenstone Track represents a low avalanche risk, compared with Milford, or Routeburn tracks, and it shows this time of year that risks are present."
Up to 2m of snow fell on high mountain areas and passes, west of the main divide, during 10 days of storms in late September.
Mr Evans said the spring snowfall, followed by sunny warm weather, was creating an ideal situation for spring avalanches, ranging from relatively minor slides to "climatic avalanches", where the entire snow pack gives way.
"Avalanche activity is a complex phenomenon, something that isn't confined to mountain tops, or alpine areas, so [trampers] need to liaise with Doc at this time of year."
The signal came only two weeks before tens of thousands of trampers set off on Routeburn, Milford and Kepler tracks.
