The Rimutaka Hill Road north of Wellington reopened on Sunday afternoon, but police said difficult conditions remained.
The section of State Highway 2 was closed on Saturday night, due to heavy snow, which then turned to ice.
Vehicles became stuck on the hill on Saturday and had to be escorted down by road works staff.
In addition, a truck and trailer jack-knifed but no injuries were reported.
The Desert Road on the central plateau is still open, despite snow on Saturday night.
In the South Island, delays were still being experienced on State Highway 1 from Kaikoura to Cheviot over the weekend because of a slip brought down in recent storms.
Motorists heading over the Crown Range in Central Otago at the weekend were advised to carry chains, because of snowfalls.
The New Zealand Transport Authority is warning drivers to watch for ice and grit on all North Island and South Island roads.