Motorists are facing a diversion of around 60 miles following a landslide near the Rest and Be Thankful.
Road management and maintenance company Bear Scotland said the landslide happened on the A83 at Butterbridge, between the Rest and Be Thankful and Glen Kinglas in Argyll and Bute.
Police said the Old Military Road diversion which is often used as an alternative route is not in use on this occasion.
Traffic is being diverted along the A819, A85 and A82, which means some motorists will face a journey of around 60 miles.
Bear Scotland said its operational emergency team is on site assessing the situation.
It said this will also require a geotechnical inspection in daylight before a clear-up can begin and resources are being mobilised for this.
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