A massive slip will see State Highway 11, which links Paihia and Kawakawa, in the Bay of Islands closed for at least two weeks according to the NZ Transport Agency.
A slip, approximately 80 metres long, occurred yesterday, blocking the road just north of Kawakawa in the Lemons Hill area.
The Transport Agency says a detour via State Highway 10 will add an additional 10-20 mins to the journey between Paihia and Kawakawa.
The early assessment from engineers is that it could take at least two weeks of work to make the hillside safe enough to reopen the road to traffic, says the Transport Agency's System Manager Steve Mutton.
"A lot depends on the weather. It's fine right now, but there have been days of heavy rain and more is forecast next week. More rain could potentially see the slip start to move again.
"We have started initial work on the slip and we must ensure the safety of our crews. Our engineers will be using a drone to help survey the extent of the slip," Mr Mutton says.
All other State Highways in Northland are open and crews are out checking roads for potholes and other road damage caused by surface flooding in recent days.