Southern police communications Shift Inspector Rick Jury said: "We have a search going on as a result of a report by a member of the public that they heard a distress call on the radio channel.''
Mr Dury said Coastguard, a police team and a helicopter were now all involved in the search.
About 4.30pm, a request for a 111 call was issued on an emergency radio channel in the Lake Wakatipu area
.Senior Sergeant Ben Butterfield said police had been unable to contact the person who made the call for help.
"We've tried, heaps," he said.
"That's all that we've been told.
"There's no information about what this person wants 111 for or where they are."