Heavy rain has caused further landslips above the A83 at the Rest and Be Thankful in Argyll.
Engineers have managed to secure the last of three boulders left exposed above the road, which has been closed since Tuesday.
But contractors Bear Scotland confirmed a storm at about 08:00 caused further secondary slips on the hillside.
A fresh assessment will have to be before the Old Military Road alternative route can be reopened.
On Thursday engineers used hydraulic gear to drill into the rocks and break them into smaller pieces.
The largest boulder, which was 300m above the roadside, was estimated to weigh about 75 tonnes.
A 60-mile diversion has been in place since Tuesday and the A83 and Old Military Road remain closed.
Bear Scotland said more than 2,500 tonnes of landslide debris reached the catch-fences above the carriageway during severe weather in the area.
Tommy Deans, Bear Scotland’s north west network manager, said “everything possible” is being done to get the Old Military Road open.
He added: “We encourage road users to follow the diversion route via Dalmally in the meantime, and to plan ahead by checking the Traffic Scotland website for up to date journey information.”
On Thursday local SNP MP Brendan O’Hara has called on the Scottish government to provide more investment to tackle the transport and economic problems surrounding the A83.
Mr O’Hara said: “Closures of the A83 leads to untenable diversions and rerouting of traffic onto other roads which are simply not designed to withstand these volumes of traffic.
“A solution to infrastructure investment to stem the flow of people and investment from the west coast must be found as a matter of urgency.
“The rural west of Scotland had suffered decades of underinvestment and depopulation and while I’m extremely grateful for the work the Scottish government have done thus far at the Rest and Be Thankful, we need a permanent solution and that means investment.”