A section of State Highway 1 on the Waikato Expressway is now closed after a number of crashes on the fog-affected road.
Heavy fog has resulted in "multiple crashes" on the expressway, initially closing both southbound lanes early this morning.
Now police have said the highway near Hampton Downs is closed to traffic in both directions while the road is cleared.
Emergency services earlier responded to reports of at least two crashes - one involving a truck.
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Waka Kotahi NZ Transport Agency is warning motorists of heavy fog in the area and asking that they delay their travel, if possible.
"Due to multiple crashes on this section of State Highway, the southbound lanes are closed.
"Visibility is poor in this area due to fog. Expect delays or avoid the area if possible."
A Twitter alert was put out just after 6am. The area affected is between Meremere and Hampton Downs.
Police say no injuries have been reported at this stage.
Motorists are reporting that they are being turned back to Auckland as a result of the crashes.