The AA, who first reported the incident at 5.36am this (Wednesday, June 29) morning, said the road is closed and delays and queues have formed due to a one-vehicle crash between A280 Long Furlong (Findon Roundabout) and the Washington turn off.
The serious crash is affecting traffic between Worthing and Horsham.
Congestion from the Long Furlong Approach stretches back to Clapham but a detour is currently in operation, the AA added.
West Sussex Highways has also advised commuters to ‘please avoid the area and seek alternative routes’.
The AA has also reported severe delays in the surrounding area.
There are severe delays of 20 minutes, and delays are increasing, on the A24 Findon By-Pass southbound between Washington Bostal and A280 Long Furlong (Findon Roundabout). The average speed is currently five mph.
There are also severe delays of 15 minutes on the A280 Long Furlong northbound between Michelgrove Lane and A24 Findon By-Pass (Findon Roundabout). The average speed is five mph.
And there are severe delays of 14 minutes on the A24 Findon By-Pass northbound between Hillview Rise and A280 Long Furlong (Findon Roundabout). The average speed is five mph.
Delays of nine minutes have been reported on the A280 Long Furlong southbound between A24 Findon By-Pass (Findon Roundabout) and Long Furlong Lane. The average speed is ten mph.
West Sussex bus company Compass Travel said the crash has delayed or cancelled some of its services.
Posting on Twitter, a Compass Travel spokesperson said: “Good morning. Some of our services are delayed this morning due to an accident closing the A24 between Findon and Washington. All services are operating, but may be subject to delays. In particular services 62, 89 are running between 25 and 45 mins late.
"We are sorry, but due to an accident closing the A24 between Findon and Washington, the Collyers Student Service is unable to serve Washington this morning.”
Sussex Police, West Sussex Fire & Rescue Service and South East Coast Ambulance Service have been contacted for more information.