The A27 remains closed in both directions near Arundel following a serious collision involving three vehicles last night.
The crash happened close to the junction with Poling Street, with National Highways confirming that one of the vehicles overturned.
Emergency services attended the scene and police collision investigators are continuing their enquiries into the circumstances surrounding the incident.
Recovery work is also underway, while National Highways contractors carry out traffic management and prepare to clear the carriageway.
Drivers are being diverted away from the affected section of the A27 using the A280, A259 and A284. Motorists travelling through the area are being warned to expect delays and are advised to allow additional time for their journeys.
In a social media update issued last night, Arun Police said: "Emergency services are currently at the scene of a serious collision at the junction of Poling Street and the A27, Arundel Road.
"Highways are supporting a road closure in both directions, and we ask drivers to avoid the area where possible at this time."
West Sussex Fire and Rescue Service also confirmed crews had been called to the collision.
Posting on Facebook, the service said: "We are currently in attendance at a road traffic collision on the A27 at Arundel.
"A road closure is in place westbound.
"Please avoid the area"
The closure is expected to remain in place while investigation, recovery and carriageway clearance work continues.
National Highways has not yet confirmed when the road is likely to reopen.
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