The race is on to clear a landslip from State Highway 6 between Wanaka and Haast before the summer season starts.
The New Zealand Transport Agency (NZTA) said it will be another fortnight before they will know when the popular Otago tourist highway can fully re-open.
"The weather's probably our biggest enemy, so when we get a rainfall that moves material, then we're back into trying to regain some control of the face," said geotechnical engineer Rob Bond.
Workers are waging a daily battle to clear the slip, which first appeared three weeks ago and is now 100 metres high.
With a steady stream of debris coming down the face of the slip, workers built a four-metre high barrier which has allowed one lane to stay open. The nearest detour is through Arthurs Pass and Hokitika, turning the 140 kilometre drive from Wanaka to Haast into an 880km haul.
North of the slip at Makaroa, night-time closures of the road have left travellers stranded.
But Michelle St John from the Makaroa Visitor Centre said "staff have been wonderful" in giving travellers accommodation for the evening.
Businesses in Wanaka are also keeping an anxious eye on the clearing work, with some owners considering the closure "a real issue" if it carries on to Labour weekend.
NZTA area manager John Jarvis said the highway is "extremely important to the tourism industry, the West Coast and feeding central Otago and the Queenstown area".
The road is now open to one lane around the clock, but it will be mid-October before anyone can predict when it will be fully cleared.