Police received a report of the incident just before 5.30pm on Sunday.
One of the man's companions raised the alarm by phone but the area is extremely remote and cellphone reception was an issue, they said.
A search operation commenced at about 7am on Monday morning involving police, LandSAR and other volunteers.
A search and rescue operation is under way after a rafter went missing on the Ahaura River on Sunday. Photo / SuppliedApproximately 17 people were assisting with the search.
Three field teams are searching the riverbanks, a jet boat is searching the river and a helicopter is conducting an aerial search.
The Police National Dive Squad will also be assisting with the search.