The A283 is "expected to remain closed for some time" after a crash.
Police, fire and ambulance crews are currently on the scene of the collision between Steyning and Shoreham.
An AA traffic report is warning drivers to expect slow traffic in the surrounding area as a result of the road closure.
A West Sussex Fire and Rescue Service spokesman said: "Please avoid the A283 between Steyning and Shoreham this afternoon.
"Our crew from Shoreham Fire Station is in attendance at the scene of a road traffic collision alongside colleagues from the South East Coast Ambulance service and Sussex Police.
"The road is expected to remain closed for some time."
⚠️
— West Sussex Fire & Rescue Service (@WestSussexFire) March 29, 2021
Please avoid the A283 between Steyning and Shoreham this afternoon.
Our crew from @ShorehamFire are in attendance at the scene of a road traffic collision alongside colleagues from @SECAmbulance and @sussex_police.
The road is expected to remain closed for some time.
⚠️
An AA traffic report from the area states: "The road is closed and there is slow traffic due to a crash.
"The collision involved four vehicles on the A283 Steyning Bypass both ways from the A27 Shoreham Bypass (at the Steyning turn off) to the A2037 Shoreham Road.
⚠️ Due to an accident on A283 and the Police closing the road, our #BH2 services which operate to/from Steyning are having to terminate and restart from Shoreham High Street until further notice We cannot serve any stops between Shoreham High Street and Steyning. ⚠️
— B&H Buses (@BrightonHoveBus) March 29, 2021
"This is affecting traffic travelling between Shoreham by Sea and Steyning."
Sussex Police have been contacted for comment.
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