The A83 has now been closed six times since December 2011, and roads management firm BEAR Scotland called in specialists to clear the area after heavy rain brought rocks and mud from a nearby hill on to the road surface.
Two parts of the road were affected and engineers are to remain at the site near the Rest and Be Thankful, in Argyll, overnight with more rain expected.
Concrete retaining blocks are to be fitted and BEAR will patrol the road to check for any danger.
Earlier today First Minister Alex Salmond described it as a "serious and developing situation". Rainfall of 26.4mm fell overnight in the region, with most of its falling between 6am and 9am.
In February a relief road to take traffic away from the notorious landslip area was opened but the new route, along an old military road in Glen Croe, was not accessible from the recent site and a detour of around 50 miles was put in place.
Transport Minister Keith Brown said: "We know that the A83 is a vital route for people living and working in Argyll and Bute and our operating company, BEAR Scotland, has deployed all of its resources to clear the hundred tonnes of rock and mud from the road at Glen Kinglas as quickly as possible.
"The slip at the Rest and Be Thankful was much smaller and unfortunately another slip caused some debris to fall on the Old Military Road which is used as a diversion route for the A83. This wasn't brought into play today as the main landslide was too far west for it to be used.
"Landslides are naturally occurring events, we can't stop them happening but we can lessen the impact and we have been making improvements, not only to our processes but also through engineering. There are no overnight solutions to the issue but we are committed to a programme of on-going works to remedy the situation.
"We have invested £3.7m in mitigation measures on the A83 including protective netting, a new culvert and drainage system at the site of a previous landslide and geotechnical monitoring equipment.
"This area at Glen Kinglas is part of the further studies we are undertaking on the A83 to find solutions to the unique challenges that the route poses."
Brian Gordon, BEAR Scotland's managing director, said: "Our team has worked flat out in difficult conditions to re-open the road. We are doing so with traffic controls and a number of other safety measures in place given the on-going poor weather forecast.
"As always the safety of motorists is our utmost priority and we will ask anyone experiencing delays to be patient while we continue to monitor the situation throughout the night."
Argyll and Bute Council leader Dick Walsh said there are concerns about the route with businesses relying on it for deliveries and trade.
He said: "Following today's closure of the A83 trunk road, we have written to Transport Scotland seeking confirmation of the suitability of the risk assessment and contingency planning for the A82 works at Pulpit Rock.
"The people who visit, live and work in Argyll and Bute depend on these lifeline routes and we need to ensure that they are able to continue to go about their business.
"We will, of course, offer any assistance that we can to Transport Scotland and work closely with them and the police to find the best possible solution for everyone."