A truck and trailer is blocking both north and southbound lanes of the Waikato Expressway following a crash that scattered debris across most of the motorway.
Meanwhile, a person was critically injured in a serious crash in the Auckland suburb of Glen Eden that was also causing delays for motorists.
Northbound and southbound lanes are closed at the State Highway 1 crash near Paddy Rd, Rangiriri and motorists are being asked to avoid the area if possible.
Police said the truck hit a barrier, continued over it and then struck an overbridge at about 3.15am this morning.
Occupants of the truck were not injured, but a "significant" amount of debris was covering the road and blocking it in both directions.
A crane has been sent to help clear the road.
In Auckland, a person was seriously injured after a crash between a car and a van on Great North Rd in Glen Eden at 6.35am.
The driver of the car has been taken to North Shore Hospital in a critical condition.
A second person was transported to hospital in a moderate condition.
The road has now been closed in both directions while a crash investigation is completed.
"Westbound cordons at Archibald Rd and eastbound cordons in place at Sabulite Rd," NZTA said.
Motorists are asked to take alternative routes where possible, to avoid significant delays.