A 38-year-old man has had emergency surgery in Auckland's Middlemore Hospital after a collision between his motorcycle and a car travelling in the wrong direction.
Police say the driver of the car did not stop after the crash.
They say they received several calls from alarmed motorists before and after the collision, which happened on the southern motorway at 1am on Friday.
Callers reported the vehicle travelling north at speed in the southbound lanes.
Police are speaking to a man whose car hit a tree on the Princes St southbound on-ramp at Otahuhu a short time after the crash.