The Manawatu Gorge road between Palmerston North and Woodville has been closed by slips and likely to remain closed for three weeks.
NZ Transport Agency Highway Manager Ross I'Anson said there are two slips: one of about 200 cubic metres at the southern end expected to take about a day and a half to clear and a much larger slip of about 3500 cu m at the Woodville end.
Early estimates are that it could take contractors three weeks to clear the larger slip and make the road safe again.
The northern slip is small compared to a large slip in 2011, which closed the road for 16 months.
"Geotechnical engineers and Transport Agency staff have done a preliminary assessment of the slips with a drone flyover, ensuring that it is safe for crews to start clearing slip material and stabilising the slopes.