Traffic is backed up for about 9km after an incident near Spaghetti Junction.
The incident happened about 12pm at the Southern Motorway link to the Northwestern Motorway, westbound.
Drivers were asked to avoid the area and consider using an alternative route.
The New Zealand Transport Agency said at 1.25pm the road had reopened but traffic remained heavy between Penrose and the State Highway 1 link - a journey of about 9km.