A police media spokeswoman said the couple were late yesterday afternoon.
Alpine Rescue Team member Chris Prudden said they were at the Esquilant bivouac this morning, about 2,200 meters on the Mount Earnslaw side, and they were supposed to be safe and sound.
Mr Prudden, who was part of the operation but was not yet actively searching, said four people from Queenstown were sent to locate the pair after the alarm was triggered by someone else.
“They had embarked on a fairly long trip that was to cross the Dart River and up Bedford Creek and across Mount Earnslaw, so it was a pretty big trip that they had planned, and given the very changeable weather we have had lately, there’s probably a good reason they’ve been delayed.
“This is not your average trip to Mount Earnslaw, put it that way.”
Mr Prudden described it as a “technical trip” which had proved fatal in the past.
Experienced mountaineer Simon Bell, of Wellington, set out from Esquilant bivouac with the intention of climbing the western summit of Mount Earnslaw, then crossing to the eastern summit on January 15, 2015.
His former partner sounded the alarm on February 2.
His body has never been located.
Mr Prudden said Mr Bell was a “very competent mountaineer” and incidents like this “always make you think”.