The A3M is now clear after crash near junction 4, near South Downs College and Asda.
A car flipped on to its roof on the northbound carriageway after colliding with another vehicle.
Queues stretched back to the A27.
Firefighters from Cosham, Havant and Waterlooville were called, and the air ambulance was also sent out. The fire service said that nobody was trapped in either car.
The Highways Agency had recommended that drivers avoid the area.