The road was shut last night after a lorry overturned at around 8.30pm and shed its load of tarmac.
According to the AA this morning the section of road is shut as emergency repairs are carried out.
The AA said the road is closed both ways between Picts Lane and Wineham Lane.
It said on its traffic news section on its website: “A lorry overturned around 8.30pm last night and has spilt tar onto the road. The road is expected to remain closed into the weekend.”
The diversions are using the A281 Henfield Road, A2037, A283, A27 Eastbound, A23 Northbound and A272 Bolney, West Sussex Highways said.