A silver Suzuki Ignis and a black Ford Focus collided at the junction, with the driver of the Suzuki losing his life. The passengers, who are now in a critical condition at the Princess of Wales hospital and Morriston Hospital, were attended to by paramedics at the scene.
A spokesman for Mid and West Wales Fire and Rescue Service said at the scene: “One person was trapped and was extricated using hydraulic cutting equipment, by the fire service and ambulance.”
The carriageway was closed for four hours, while officers undertook the early stages of their investigation. Anybody with information is asked to contact South Wales Police Roads Policing Unit in Gwaelod y Garth, Cardiff on 02920 633438 or 101.