Stock photo of the A27 at Patcham (Image: The Voice of Hassocks)
Motorists are facing standstill traffic and part of the A27 is closed.
An on-going police incident means the A27 eastbound at Patcham is closed and traffic is stationary.
The incident took place between the A23 London Road and Carden Avenue at the Hollingbury / Ditchling junction.
The road was closed for around two hours.
At 4.30pm, Brighton and Hove police tweeted: "We have now re-opened the A27 near the Coldean / Lane Ditchling Road area in both directions following an earlier closure while we dealt with an incident near the bridge."
Sussex Police have been contacted for comment.
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