Police have closed the A24 southbound between Washington and Findon after a lorry struck a crash barrier and ruptured its fuel tank, spilling a large amount of diesel across the carriageway.
The incident occurred just before 6.30am today (Tuesday) and involved a Volvo refrigerated truck.
It suffered nearside damage after colliding with a barrier near the Windlesham House overbridge, near Findon.
At 8am police said it could be "some time" before the spillage was leared and the road re-opened.
Motorists are being advised to avoid the area and to seek alternative routes.
Sgt Phil Duffy, of Sussex Police's road policing unit, said: " As well as the skid danger, the diesel oil is also thought to have damaged the road surface itself. Highways and Environment Agency officers are currently examining the scene.
"Clearly it's a busy time of day for this to have happened, and I would like to thank drivers whose journeys have been affected for their patience."
Anyone who saw what happened to the lorry just prior to the spillage is asked to phone Sussex Police on 101 or email firstname.lastname@example.org, quoting serial 162 of 19/8.