ITV News has been speaking to Davina Payne, who drove past the crash minutes after it had happened.
Traffic was at a standstill past the Brynglas tunnels going Eastbound. The coach was situated between the slip road to Caerleon and the slow lane. I could see passengers standing around - some were still in the coach and there appeared to be a person still sitting behind the wheel. The whole of the front of the coach had been taken off - there was mangled and twisted metal everywhere. There was a white car in the fast lane at a right-angle across the motorway.
More top news
The Lesbian, Gay, Bisexual and Transgendered communities in Cardiff are celebrating 30 years of campaigning; as part of LGBT History Month.
Cloudy at first, with outbreaks of rain gradually easing during the morning.
A grey and damp start today. Rain will turn heavy and persistent late afternoon and winds will increase overnight.