The crash happened between junctions 11 and 12 of the eastbound carriageway, blocking two lanes.
Hampshire Constabulary has since handed over to Highways Agency, who has re-opened both lanes after clearing an oil spillage.
However, traffic alert service Romanse has warned commuters that diversion routes remain very congested, although delays are now starting to ease.
Traffic is also moving slowly on the westbound carriageway from the M27 and A3(M), while diverted cars are causing tailbacks on the A27 between Segensworth and Fareham.
South Central Ambulance Service said it was called at 6.56am to an incident involving five cars and an motorcycle.
A spokesman said the motorcyclist had suffered neck, arm and leg injuries and that two other people had minor injuries.
He said that three ambulances, two rapid response vehicles and a hazardous area response team were at the scene.