Police are searching the Manawatu River in Palmerston North after a report of a man in trouble in the water.
Emergency services were called about 1.35pm with a report that a man walking his dog at Ahimate Park had fallen into the river.
When the man failed to reappear, his walking companion alerted emergency services, police said.
A search began involving Police Search and Rescue staff, a Swift Water Rescue boat, kayaks, drones, a helicopter and numerous other volunteers.
Crews are currently working to locate the man and will continue until dark, police said.
The Police National Dive Squad has also been notified.