One person is dead after the single-vehicle crash at the intersection of SH1 with Bushey Park Rd about 3am.
The driver, the sole occupant of the vehicle, died at the scene.
Police were alerted about 4.25am, and the highway was closed for several hours.
In a statement this afternoon police said they were appealing for information, and particularly wanted to speak with a motorist who arrived at the scene and waved down a truck driver who then called 111.
Anyone with information was asked to contact Oamaru Police on 03-433 1400.