A lorry and car have crashed on the A27 Brighton Bypass and the road has been closed in both directions.
The accident happened near the Southwick Tunnel on the eastbound side of the road.
The lorry left the road and ended up overturned, facing the oncoming traffic on the westbound side of the road.
Sussex Police described that accident as “a serious collision” and two air ambulances have landed on the road.
One driver stuck in the long tailbacks said that at least two fire engines and four ambulances were also at the scene.
Traffic was queueing on the A293 link road, the A2038 King George VI Avenue, known locally as Snakey Hill, and Dyke Road Avenue and Devil’s Dyke Road.
Sussex Police said: “A serious collision has led to the A27 being closed near the Southwick tunnel.
“Two air ambulances attended after a lorry and car collided on the eastbound carriageway after leaving the tunnel.
“The lorry then left the road and ended up on the westbound carriageway.
“Both carriageways are closed and will be for some time. Diversions have been set up and motorists are asked to avoid the area.”
