The Police National Dive Squad will join the search for the missing swimmer at Omanawa Falls tomorrow.
Police Search and Rescue were called to the falls at 2.55pm after a report a person was "missing in the water", a police spokeswoman said.
Police were able to help two people from the water, but a third person remained unaccounted for.
Council staff are limiting access to the area overnight, before searches resume in the morning.
A police spokeswoman said police were alerted to a "report someone's missing in the water" at 2.55pm.