State Highway 1 north of Auckland has re-opened after a milk tanker crashed just north of Puhoi closed it for 12 hours.
The road closed about 5am after a truck crashed, spilling thousands of litres of milk fat over three lanes of the motorway.
Police said milk fat which spilt onto the road solidified and formed a slippery surface which proved difficult to remove.
High-pressure water blasters were used to clear the road.
The truck driver was injured in the crash.