Crashes at both the Bognor Road Roundabout and the Tangmere Roundabout are said to be causing big delays on the A27.
The Bognor roundabout is reportedly partially blocked with traffic moving very slowly because of a two-car crash.
Traffic is backed up along the A259 towards Bognor.
And a four-vehicle crash is partially blocking the Tangmere roundabout, affecting traffic between Fontwell and Chichester.
Police are said to be at the scene of both incidents.