One eyewitness, 23-year-old Liam Llewellyn from Caldicot, was on his way home when he approached the crash eastbound around St Julians.
He told radio station Capital FM South Wales he was shocked at the number of motorway travellers who tried to continue their journeys without stopping to help, despite the obvious scale of the crash.
Mr Llewellyn said he was initially just one of four members of the public to offer assistance.
My first instinct was to call 999, I managed to get through to emergency services, but the worst bit was everyone just appeared to stay in their vehicles, and no one was willing to help.
As I was on the phone to 999, I asked them do they want me to get out of the vehicle and assess, so then at that point I went to the bus to see the driver, who was in a bad state.
Because the car had actually hit the central reservation, the lady in the vehicle wasn't being attended, so I assessed her and she was OK, but obviously quite distressed.
I don't want to go into details of what I saw, but it was something I've never seen before in my life.
[The students on the bus] didn't speak much English, they appeared to be on tour, but it was just making sure they got to safety as well, get their belongings off, and assessing them, the hand gestures, asking 'are you OK'.
I've always been brought up in an environment where you need to look after people and they'll look after you and I like to think that if I was ever in a situation like that, people would come and help me as well.
I wouldn't class myself as a hero at all, you just do what you got to do to make sure someone's safe.
But a police officer said to the people who helped: 'It's a pity there aren't more like you'.
Eleven people have been taken to hospital following this morning's crash on the M4 at Newport, it has been confirmed.
The Welsh Ambulance Service says it received a call at 9.29am after the collision, at Junction 25a to 25 eastbound at St Julians, which involved a coach, lorry and a car,
Two rapid response vehicles, two Hazardous Area Response Team vehicles, two doctors, four emergency ambulances, two air ambulances and three ambulance officers attended the scene.
The driver of the coach has been flown to Morriston Hospital with serious injuries.
A second patient has been taken by emergency ambulance to the University of Hospital Wales, also with serious injuries.
Nine patients – one with potentially serious injuries and eight with minor injuries – have been taken to the Royal Gwent Hospital. The drivers of the lorry and car were treated at the scene but did not require hospital treatment.
Forty-four other students who were travelling on the coach have been taken to a nearby rest centre where two advanced paramedic practitioners and two BASICS doctors provided further assessments.
Gwent Police has urged drivers to avoid using the M4 near Newport until the site of the crash has been cleared.
Chief Inspector Paul Evans said: “We appreciate the closure is causing problems for motorists. However, the decision to do so is never taken lightly and we fully recognise the impact this has on motorists as well as the communities affected by diversions.
“We need to ensure we investigate every such collision thoroughly, gathering all evidence possible, and also ensuring the safety of everyone involved, as well as other motorists who will be using this road once it has reopened.
"We are grateful for the understanding and patience shown by drivers and their passengers today."