The A34 southbound has been shut between the A303 entry slip road to the A272 near the Thee Maids Hill roundabout due to an RTI with delays building on the approach.
The motorway has been closed following an incident involving with ambulance and police already at the scene.
The closure is causing severe congestion starting at Bullington Cross and is said to be causing 20-minute delays in the area.
Hampshire Police and the South Central Ambulance Service have been contacted for a comment.
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