The A13 in Essex is closed in both directions after a vehicle reportedly crossed through the central reservation barrier.
The eastbound road between junctions A1012 and A1089 remains closed while the westbound route between junctions A1089 and A1012 has also been shut.
Traffic is being diverted through local routes and drivers are being urged to avoid the area.
Emergency services were called to the scene between North Stifford and Grays at 8.45pm this evening.
National Highways tweeted: "The #A13 in #Essex is BLOCKED eastbound between the #A1012 (#NorthStifford) and the #A1089 (#Grays) due to a collision involving two vehicles."
A spokesperson said: "The A13 in Essex is closed in both directions between the A1012 (North Stifford) and the A1089 (Grays) due to a collision involving a vehicle which has crossed through the central reservation barrier.
"Emergency services including Essex Police are in attendance. National Highways contractors are also on scene providing assistance with traffic management and assessing infrastructure damage."