A four-car crash has closed lanes in both directions on State Highway 2 near Lower Hutt.
The crash happened near Belmont at 2.45pm. It is understood four cars were involved.
It is not know whether anyone has been injured.
"The road is down to a single lane in both directions and motorists should avoid the area or expect delays," police said.
"Initial indications suggest there are injuries."
NZTA posted an image of traffic backed up heading north.
"A crash is BLOCKING lanes in both directions at the intersection with Owen Street. Please take extra care and expect delays."
Meanwhile, holidaymakers heading home elsewhere are being urged to stay calm on the roads as traffic congestion builds in some areas.
The NZ Transport Agency said just before 4pm congestion remained heavy heading north between Drury and Takanini, South Auckland.
"Please continue to expect delays or avoid the area,'' a statement said.
On the other side of town, congestion between Warkworth and Puhoi had eased by 2pm after earlier congestion caused delays late this morning.
Road authorities said earlier that motorists could expect "significant delays'' and, as a result, people were being told to avoid the area, if possible.
Motorists were told to consider using State Highway 16 between Wellsford and Silverdale as an alternative route.