Paramedics treated six people after two separate crashes shut the A3.
Two people were involved in a two-car crash between a Citroen C3 and another car and another four hurt minutes later in a four-vehicle crash.
Police said one person was seriously injured in the first crash, which happened on the southbound carriageway at 11.59am.
Firefighters had to cut two people out of the vehicles.
The A3 was shut in both directions at Clanfield after the separate crashes at Chalton Lane.
A four-car crash between a Citroen Berlingo, BMW, Lexus and another vehicle at 12.45pm led to the closure of the northbound carriageway.
A South Central Ambulance Service spokeswoman said two people in the four-vehicle crash were taken to Southampton General Hospital, while two were treated at the roadside.
Two casualties in the two-car crash were taken to Queen Alexandra Hospital.
Fire crews from Waterlooville, Cosham and Emsworth cut two people out their vehicles in the first crash.
Delays of around 65 minutes were reported.