Large cavities in a rock face at Ruato Bay have led to a delay in the road being re-opened completely.
The New Zealand Transport Agency said the section of State Highway 30 had experienced some unexpected challenges.
The section of road was closed due to a rock fall in August 2012. The crew have been working to a Christmas deadline, said highways manager Brett Gliddon, but they've encountered issues with grouting the last several hundred holes because of large cavities within the rock face.
"The crew have been working overtime to try and remedy the issue with grout and approximately 400 holes have been filled, the bolts secured and a significant amount of protective steel mesh has been placed along the site," he said.
"There are another 120 holes to be filled which will not be completed before Christmas, despite the crew's efforts. Once the wire mesh fencing is secured, and the danger of further rock falls is reduced, then the road is safe to open up to two lanes and this is likely to be early next year."
The current signalised traffic management operation will be in place throughout the summer holiday period and until the project is completed.
The works involve drilling 500 holes into the rock face and filling them with concrete to secure the rock face.