The northbound carriageway has been closed and a diversion is in place following the collision, which happened just after 10am.
A Sussex Police spokesperson said minor injuries have been reported from the incident.
Reports suggest the vehicles involved two vehicles, including a cement mixer.
Emergency services including three fire engines and multiple South East Coast Ambulance Service vehicles have been called to the incident.
A spokesperson for West Sussex Fire and Rescue Service said none of the drivers were trapped in their vehicles.
Images taken from the scene show that one lorry appears to have left the road.
The incident happened between Pyecombe and Hickstead. Northbound traffic is being diverted off at the junction with the B2118, leading to Albourne and Hurstpierpoint.
The police spokesperson said: “Motorists are encouraged to find other routes.”
The road is likely to be closed until at least 2pm for recovery work.
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