The emergency services are on the scene of a motorway crash involving a car and a petrol tanker.
Police, fire and ambulance crews are at the incident near junction 44 (Llansamlet) of the westbound M4, and one lane is blocked.
Mid and West Fire and Rescue Service say the petrol tanker has not been breached, and no fuel is leaking on to the carriageway. The accident happened just before 7.45pm.
There are no details yet of any casualties.
Two fire crews from Morriston station are in attendance, and the vehicles involved are currently being moved on to the hard shoulder.