Paul Scott was in his car on the way to Asda when a pedestrian was hit by a truck at the crossing around 11.30am.
He told the Mercury: “I was at the lights waiting to turn right towards Asda. The truck was coming from Asda waiting to turn right toward Sainsbury’s.
“It looked like the person who was hit must have stumbled or tripped from the crossing into the side of the lorry.”
He praised the quick response of emergency teams.
“The ambulance was already on the scene before I’d finished dialling 999. He must have been in the area,” he said.
“I don’t know what condition the man who was hit is in - but if he survives, a big part of that will be because of that paramedic.”
The Mercury has asked police for an update on the condition of the man - but is yet to receive a response.