The southbound lane of State Highway 2 at Rimutaka Hill near Wellington was temporarily blocked by a slip south of the summit.
The NZ Transport Agency reported the incident at 5.30pm and announced at 6.20pm a stop/go control was put in place.
Emergency services are at the scene on the Upper Hutt side of the hill and the NZ Transport Agency is advising motorists to expect delays.
(Rimutaka incorrectly spelt Remutaka in tweet).
Meanwhile, the Northern Motorway in Auckland is heavy for citybound traffic between Esmonde Rd and the Harbour Bridge.
Citybound traffic on the Southern Motorway is heavy between Ellerslie and Greenlane. Congestion is heavy southbound at Manukau and easing at Takanini.
The Northwestern Motorway is heavy but easing for westbound traffic between Patiki Rd and Te Atatu Rd.
Traffic on the Southwestern Motorway is heavy for southbound traffic approaching the Southern Link.
Major works that were being conducted on Customs St East between Fort and Gore St from 2am to 4pm on Friday have been cancelled, Auckland Transport reports.