The Snake Pass in Derbyshire will remain closed for at least a month after damage caused by torrential rain during Storm Eunice and then Storm Franklin.
Derbyshire County Council said teams are unable to come up with final repair designs until the road has stabilised.
It is due to be closed for a month but could be shut for longer.
Derbyshire County Council’s Cabinet Member for Highways Assets and Transport, Councillor Kewal Singh Athwal, said:
"I know this will be a huge inconvenience to everyone who uses the A57 regularly.
“However, with the ground underneath the road surface expected to continue to move, in the interests of everyone’s safety we simply cannot allow traffic to use the road.
"This is an evolving situation but please be assured we will continue to monitor the situation closely.
"Once the land movement has stopped we will assess what needs doing to repair the sections of road. However, once in a position to do this it will be a complicated piece of work.
"I’d like to thank everyone for their patience as we deal with the aftermath of this unprecedented weather which has affected not only Derbyshire but much of the country.”
Local access will still be kept for local residents but other drivers are being asked to follow the diversion route through Hathersage, Hope, Doveholes, Whaley Bridge, New Mills, Hayfield.