One casualty suffered serious injuries in the accident between two cars.
It happened at the Rusty Cutter roundabout at Bedhampton at 8.30am.
At 10am police said that traffic was flowing along the A27 despite earlier reports that it had been closed in both directions between Bedhampton and Havant.
But long delays soon built up on the A3M southbound after the crash.
And Hulbert Road was very congested towards the Purbrook Way roundabout as traffic diverted from the A3M.
South Central Ambulance Service said it helped six patients, two of whom were treated at the scene.
Three patients were taken to Queen Alexandra Hospital, Cosham, with minor injuries, while the sixth person was taken to the same hospital with serious, but not life-threatening, injuries.
The Hampshire and Isle of Wight Air Ambulance was called out and landed in a nearby field but was not needed.
Main picture by Harry Lewis
Second picture by Eleanor Carver shows southbound traffic queued on the A3M after the accident