The road between Haast and Lake Moeraki was closed just over a week ago when record-breaking rain pummelled the region, causing slips, rockfall and cracking in the highway.
More wet weather last week had hampered the repair job, but conditions cleared up over the weekend, NZTA central South Island system manager Mark Pinner said
"The crew was able to use the helicopter to sluice the highest parts of the rock face on Saturday and has completed most of the safety-critical rock removal over the past two days," he said.
On Monday, crews will use that rock to build a bund around the base of the cliff face to reduce the risk of any future rockfall making it on to the road.
Cracks in the highway will also be filled this week and drainage improvements installed to funnel water away from the area.
The road closure was frustrating for West Coast and Otago hospitality and tourism operators who rely on the Haast / State Highway 6 loop for much of their summer business, he said.
"We are doing our best to return this road to everyone in a safe condition, ready for the months ahead."
The transport agency would provide an update on Wednesday including a timeline for reopening the road.