The M4 was closed in both directions at Margam after a “serious collision” overnight.
South Wales Police are at the scene of the crash and motorists are advised to avoid the area.
The road has been closed westbound between junction 38 Margam and junction 39 Groes.
Eastbound the road was closed from junctions 40 to 38 but has since reopened.
The Welsh Ambulance Service said it was called at around 2.22am to reports of a road traffic collision between junctions 38 and 39.
Traffic Wales, the Welsh government’s motorway and trunk road information service, said there are delays of around one hour on surrounding routes.
The road is expected to remain closed for some time.
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A Welsh Ambulance Service spokesperson confirmed it had taken one patient to the University Hospital of Wales in Cardiff for further treatment.
“We sent one duty operational manager, one hazardous area response team and one emergency ambulance to the scene where we were supported by colleagues from the Emergency Medical Retrieval and Transfer Service who travelled by car and pre-hospital immediate care specialists from MEDSERVE Wales,” the spokesperson added.
