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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It is now believed that 45-year-old Robert Cantle may have travelled in his car to the Jedburgh area on Sunday morning.
A Cumbrian man has been jailed for 15 years after a police crime unit seized its biggest ever haul of firearms.
The historic event always takes place on the last Friday in July.