The A270 Old Shoreham Road in Portslade is partially blocked because of an accident involving an overturned van and a car.
The westbound carriageway between the B2193 Trafalgar Road junction and the Mile Oak Road junction is blocked. The accident, near the Mayberry Garden Centre, happened at around 7.20am.
The road is closed. Sussex Police said there were no reported serious injuries.
There are diversions in operation for Brighton and Hove Buses 2, 2A and 46 via Trafalgar Road.
A spokesman from Sussex Police said: "Police were called at 7.24am to a collision between a car and a van on Old Shoreham Road in Portslade, near to the garden centre.
"The road was closed in both directions as the vehicles were recovered. There didn't appear to anyone injured."