Angus is in the middle of a "very serious emergency" as "unprecedented" record-breaking flooding caused by Storm Babet continues.
Residents have been warned to evacuate their homes if they believe they are in danger of flooding, as the red weather warning persists until midday on Friday (October 20).
It comes after a woman died after being swept into a river and Brechin residents were ordered to evacuate following the extreme rainfall which arrived in Scotland on Thursday.
Humza Yousaf said he "cannot stress how dangerous conditions are in Brechin in particular".
The First Minister urged people to follow the advice of Angus Council, which has told people not to travel in the severe conditions.
The authority said: "Angus is in the middle of a very serious emergency. Flooding is unprecedented. Levels are over half a metre over the last highest EVER.
"Most roads are affected. A90 is closed in both directions and is not passable for any have-a-go heroes. DO NOT TRAVEL!"
Brechin defences were breached at around 4am on Friday morning, the council said, with river levels around 4.4 metres above normal.
Parts of Brechin and other parts of Angus are now only accessible by boat, the council said, with rescue crews dealing with around 100 calls from areas asked to evacuate.
"If you think you are in danger of flooding, PLEASE DON'T LEAVE IT TOO LATE," the council said.
Three rest centres have been set up at Montrose Sports Centre and Brechin and Forfar community campuses, with pets welcome.
People have been advised to stay at home and not to travel unless ordered to evacuate.
Meanwhile, amber and yellow weather alerts for heavy rain and strong winds cover vast parts of Scotland into Saturday (October 21).
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