Reopening the Manawatu Gorge road is now expected to cost $10 million and take at least until the end of January.
NZ Transport Agency state highways manager David McGonigal said work had begun on benching the slip - now estimated at 200,000 cubic metres - from the top.
Debris would then be trucked away and used as a base for other projects. The amount to be removed was estimated at 20,000 truckloads.
So far, the agency had spent about $5 million on the gorge and $2 million fixing local roads.
Mr McGonigal said staff were working in tough conditions.