Two people are believed to be on board a helicopter reported missing in the Awarua area, near Invercargill, on Thursday afternoon.
The search for the aircraft, which was on a training flight, is continuing into the night.
The Robinson 22 was reported overdue at 2pm after nothing had been heard from it in the previous half-hour.
Three helicopters are searching more than 1000 square kilometres east of Bluff, using night-vision equipment.
Nick Churchouse from Maritime New Zealand says it's a widespread search. The Rescue Co-ordination Centre say two helicopters, police and the Coastguard are taking part.
Through maritime radio, vessels in the area off Invercargill have been asked to be alert for possible sightings.
