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.
"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.
"More detailed analysis will now be done and a further meeting between the Transport Agency and engineers tomorrow at 9am will decide on the next steps," I'Anson said.
Motorists can use the Pahiatua Track and the Saddle Road as alternative routes.
Motorists can check the latest information on highway conditions, delays and closures at www.highwayinfo.govt.nz (external link) , or by calling 0800 4 HIGWHAYS (0800 44 44 49).