The A27 westbound has been closed following a collision at Selmeston, according to Sussex Police
Police have advised motorists to seek alternative routes if they can, as it is likely to be closed for at least a couple of hours.
The eastbound carriageway remains open.
In a tweet, Sussex Police said: “Thank you for your patience and understanding.”
The A27 westbound is also closed due to a two vehicle collision at Lewes.
Traffic is blocked from the A26 (Southerham Roundabout) to the A275 Brighton Road (Ashcombe Roundabout).
Congestion has been reported to Beddingham.
Traffic is queueing through Lewes as it diverts past the closure, according to traffic reports.