Two large rocks, that were hampering efforts to clear a massive slip blocking Awatere Valley Road in Marlborough, have been blasted using 100kg of dynamite.
The blast took place yesterday, and was shot on video.
A water cannon capable of sending high pressure water up to 70m arrived on-site from Christchurch yesterday and joined the effort to clear the slip today.
State Highway One south of Clarence remains closed.
Crews are also working to open both lanes on Queen Charlotte Drive by the end of the week. The road has been down to one lane in places and patience is urged.
The 100km-long Awatere Valley Road connects coastal Marlborough to Molesworth, New Zealand's largest high-country station, and on to Hanmer Springs.
The slip, which was formed after the magnitude 7.8 Kaikoura earthquake on November 14, is so unstable it's described as a dangerous site to work on.
Nine families remain isolated by the slip, though their properties can be accessed through Hanmer Springs.
Marlborough Civil Defence continues to provide supplies to these remote farms by helicopter each week.
For the first three weeks, contractors and diggers have been removing unstable rocks by either "sluicing" them with monsoon buckets from helicopters, or blasting them with dynamite using abseilers.
Last Friday, workers got the site stable enough to start excavating with a remote-controlled digger.
By last night, contractors we were able to get three quarters of the way across the slip.
However, crews had to pull back after loose material began falling from above.
"We called in helicopters to sluice again, which uncovered four huge boulders that were in a very dangerous position," Marlborough Roads' Steve Murrin told Scoop.co.nz.
"We managed to dislodge two of these, but the other two are proving very difficult to move. They each weigh in excess of 15 tonnes."
A Marlborough Roads geotechnical engineer, who worked in Christchurch on the Port Hills and Sumner rock falls, says the slip is the most technically challenging he has seen.
"It's hard to put a time-frame on when we will have the Awatere Valley Road open."