Waioeka Gorge north of Gisborne is closed by a large slip for up to a month.
The Transport Agency says about 100,000 cubic metres of dirt and rocks came down on Saturday.
The road links Gisborne to Opotoki. NZTA says drivers will need to allow for an extra two to three hours, taking the road around the East Cape or south via Napier and Taupo.
Bay of Plenty state highway manager Andrew Scott says contractors are already working on the slip. A team of experts who have worked on the Manawatu Gorge slip, will assess the site.