At this very early stage there is an investigation ongoing, which will look at all aspects of what occurred before the incident and immediately at the time of the incident.
There is a team of very experienced and expert officers in our Serious Collision Investigation Unit, who have surveyed the scene and will systematically interview all witnesses to gather that information.
At this stage it's too early to say exactly what caused the distressing circumstances that led to this collision today.
Again, I'd appeal for any witnesses to contact South Wales Police on 101.
Police have stressed that the incident is not being treated as a deliberate act at this stage.