Dyfed-Powys Police said the crash, involving a bus, happened on the A484 near the Kidwelly roundabout in Carmarthenshire.
The force added the road was currently closed between the roundabout at Parc y Bocs and Llandyfaelog, and motorists were asked to find alternative routes.
Emergency services are on the scene and members of the public have been asked to stay away from the area until further notice.
This breaking news story is being updated and more details will be published shortly. Please refresh the page for the fullest version.
You can receive Breaking News on a smartphone or tablet via the BBC News App. You can also follow @BBCBreaking on X, external to get the latest alerts.
