MOMENTS after a lorry veered off the M4 near the M4 Prince of Wales Bridge on Wednesday, motorists stopped their vehicles and scrambled down the roadside banking to help the driver.

Among them was surgeon Charlie Chan, who tried to save the driver's life by giving CPR until paramedics arrived.

"I was on my way to the Rutherford Cancer Centre when I saw all the traffic slowing down," Mr Chan said. "I could see debris all over the road, but I was thinking: 'Where's the vehicle?'

"Then I saw people looking over the edge of the hard shoulder. I could see a lorry jack-knifed at the bottom."

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Mr Chan ran down the roadside banking, and when he got to the lorry he found two people helping the male driver.

"He was unconscious, but breathing, and had a weak pulse," Mr Chan said of the driver. "It was tricky getting into the cab, and he was a big guy – we couldn't possibly lift him.

"We got him on the floor and did CPR until the Air Ambulance arrived.

"By then there were about 20 guys there to lift [the driver] out."

Mr Chan said CPR was something all doctors, nurses, and paramedics knew instinctively, but stressed that anyone could learn this vital skill.

"Learning CPR probably takes about an hour," he said. "Lots of professions offer courses, and it doesn't matter if it's somebody crashing on the motorway, somebody collapses in the street, or it's your partner at home – you can do this, it's not difficult."

Another eyewitness, Stroud councillor Chas Townley, was driving behind the lorry when it crashed.

"It veered out of the left-hand lane and hit the central reservation, then bounced back across, dropping lots of debris," Cllr Townley said.

The lorry then went off the road, into the field below.

"It's a miracle nobody was caught against the [central reservation] barrier," the councillor added. "There was a considerable amount of damage."

Cllr Townley stopped his car and immediately called the police – several other motorists were already running down the steep banking to assist the lorry driver, he said. The police asked him to stay at the scene until they arrived.

Walker Ralph Bevan had been enjoying a stroll on the Wales Coast Path when the crash happened.

"I was at a rail crossing and I heard an almighty bang as I walked through," he said. "I saw that the traffic on the bridge had slowed down."

Mr Bevan turned the corner and saw the crashed lorry in the field.

He added: "I thought 'What the hell?'

"I could see people everywhere on the banking, running down.

"I don't understand how it happened, or how he got there."

The male driver of the lorry was airlifted to the University Hospital of Wales, Cardiff, with what Gwent Police described as "serious injuries", and later died at hospital.