The aircraft was a twin-engine Beechcraft Baron and was travelling from Ardmore to Timaru.
No details were known about the people onboard.
RCC Search and Rescue mission controller John Dickson said the aircraft radioed Airways New Zealand to report engine failure shortly before radar contact was lost.
"A helicopter from Phillips Search and Rescue in Hamilton is searching the area, along a fixed-wing Coastguard aircraft, and a Raglan Coastguard vessel is also on scene and is picking up debris,'' he said.
"Unfortunately there has been no sign found of the people onboard.''
