A driver crawled from the cab of his lorry after it crashed off the road into a river at the Pont Abraham roundabout.
The accident happened early on Friday morning, and drivers who were passing at the time helped at the scene until police and first responders arrived. The lorry reportedly overshot the roundabout, which links the A48 with the M4, and crashed through the barriers before ending up in the river below.
There were long queues of traffic throughout the morning and early afternoon as recovery work was carried out at the scene. Live updates here.
Aaron Thomas was one of the first on the scene and helped the driver who had been able to get out of his cab after it ended up in 6ft of water.
He said: "The driver was not seriously injured, but he had cuts and was very dazed.
"There were two other people who also helped before police and first responders arrived on the scene."
There was also a second accident, which happened just before 11am, when a car crashed on the roundabout.
A recovery crane, brought in to lift the lorry, blocked access to one lane on the roundabout.
It has left the scene by 2pm, and motorists were able to get around the roundabout, but there were still delays of around 40 minutes in the area.
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