Emergency services have been called to the collision in Sloughgreen Lane, Warninglid.
The fire service said two people were trapped in the vehicles and were freed by firefighters.
Two others managed to free themselves from the vehicles before crews arrived.
All four have been left in the care of the ambulance service, the fire service added.
Police are at the scene and have closed the road between the junctions of Cuckfield Road and Broxmead Lane.
More to follow.
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