The incident near Shilbottle was reported at 10.29am and fire crews from Alnwick and Amble are in attendance with Northumbria Police.
Both lanes were initially closed. One lane has now reopened but the first lane will remain closed until the vehicle has been cleared.
There are no reported injuries.
Northumberland Fire and Rescue Service, in a tweet at 10.48am, posted: ‘A1 in Northumberland closed southbound due to wagon fire. Wagon fire on A1 southbound at Shilbottle, crew from Alnwick and Amble attending with @northumbriapol
‘The A1 is closed southbound.’
North East Live Traffic posted: ‘The A1 is currently closed southbound just south of Shilbottle in Northumberland due to a HGV on fire which appears to have damaged the carriageway, emergency services are at scene.’