Traffic backed up along the Solomon Hochoy Highway on Wednesday afternoon after a vehicle flipped several times and landed on the hood.
The occupants, police said, were trapped inside.
Fire officers removed the injured.
Police said the vehicle was traveling along the south bound lane, near the Macaulay overpass, when the driver lost control at around 1.30pm.
The vehicle overturned several times and crashed into the steel barriers.
The accident caused a massive traffic pile up on both lanes of the highway.
Fire officers from the Mon Repos fire station and officers from the St Margaret's police station and Highway Patrol Unit responded.