The eastbound carriageway of the M4 is closed between J38 A48/Margam offslip and J37 A4229/Pyle due to an accident. Traffic Wales is warning of delays as all three lanes are currently closed.
Both South Wales and Mid and West Wales fire services are at the scene. A South Wales Fire Service spokeswoman said it is believed three cars have been involved in a collision and a car had also broken down nearby.
A South Wale Police spokesman said there had been a number of accidents on the M4 following a hail shower. He said no one suffered any significant injuries.