A full ground and air search will begin at first light on Tuesday for a helicopter pilot missing after his aircraft crashed into Lake Sumner in North Canterbury.
The helicopter was one of two Rangiora-based Hughes 500s spraying gorse for the Department of Conservation on Monday afternoon.
When one failed to return just before 3pm, the pilot of the other helicopter returned to the scene and spotted wreckage in the lake.
The area is remote and mountainous country and the only access is by four-wheel-drive vehicles.
A spokesperson for the rescue helicopter service says conditions for flying were perfect on Monday.
Police officers will remain at the scene overnight.