Shoreham town centre has ground to a standstill following reports of a collision.
A car and a motorcycle are reported to have collided on the A259 High Street, near the Ropetackle roundabout.
Traffic is queuing in both directions along High Street, Brighton Road and Old Shoreham Road, as far up as The Bridge Inn roundabout.
In a tweet, Brighton and Hove buses said the BN2 service would terminate at Shoreham Railway Station.
Stagecoach seafront buses are diverting along Grinstead Lane and along the A27, adding to significant delays already caused by an accident in Lancing.