The A90 is shut between Dundee and Stonehaven as drivers are being urged to stay at home.
The carriageway is closed both ways due to the severe rainfall and strong winds brought by Storm Bebet.
Traffic Scotland says local access is permitted as far north as Brechin.
The official diversion route is via the A9 and A95 northbound, and the A95 and A9 southbound, but is about 150 miles long.
It has not been confirmed when the road will reopen.
A post by Angus Council said: “Due to updated severe flood warning guidance from Sepa, Traffic Scotland has agreed with Police Scotland to close the A90 between Struan’s Garage (Dundee) to Stonehaven (AWPR/A90/A92 Junction).
“Access for emergency vehicles and residents will remain northbound up to the A94 Forfar junction and southbound up to the Brechin South junction.
“Please note that the absolute closure points will be at the following points, this has been identified by Sepa’s severe flood warning maps: A90 crossover point at the unclassified access road to Carestone (southbound); A90 crossover point at the unclassified road to Bogardo (northbound).
“Flooding is particularly bad around Finavon.”
Locals are being urged to stay at home as a red weather warning is in place until noon for large parts of Angus, Dundee, Perthshire and Aberdeenshire.
It comes after a 57-year-old woman died on Thursday when she was swept into a river in Angus.
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