State Highway 35 between Tolaga Bay and Tokomaru Bay in the Gisborne district remains closed on Tuesday night.
The road was closed on Monday north of Tolaga Bay township due to concerns over the swollen Hikuwai River.
Rain overnight caused a large slip at Busby's Hill, just south of Tokomaru Bay.
A geo-technical inspection concluded that the hillside is unstable and further tests need to be done. Another assessment will be made on Thursday.
All other sections of the highway where slips occurred have been cleared.