Two casualties have been airlifted to the Southern General Hospital, with a further casualty taken by ambulance to the Dumfries and Galloway Royal Infirmary.
The Northbound carraigeway is closed and will remain so for a considerable period while investigations are carried out. The Southbound carriageway has one lane now re-opened.
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Concerns about the safety of the hospital's PFI building have been raised by the NHS Trust. The fire service says improvements are needed.