Waiotemarama Gorge Road in South Hokianga has been closed to all traffic by major slip and is unlikely to re-open fully until early August.
Waiotemarama Gorge Road cuts inland through Waima Forest from Pakanae on the Twin Coast Discovery Highway (State Highway 12) just before Ōpononi.
It re-joins the highway just west of Waimamaku. The route bypasses Ōpononi, Ōmapere and the southern headland of Hokianga Harbour.
A Far North District Council spokesman said the slip, which began during Tuesday's heavy rain, has continued to deteriorate, and has now undermined a significant section of the road.
It is located between Kelly Road near Pakanae and Smoothy Road. Ongoing rain in the area has increased the risk of further subsidence and contractors are now improving stormwater drainage around the site.