The Midlands Air Ambulance was called to the busy A449 road outside Wolverhampton city centre at around 11am.
Crews were joined by ambulance staff and police at the scene near Selco building supplies on the Wulfrun Trading Estate.
A man suffered potentially serious injuries in the crash, West Midlands Ambulance Service said.
He was taken by road to the major trauma centre at Birmingham’s Queen Elizabeth Hospital for further treatment, accompanied by the doctor from the Midlands Air Ambulance.
Diane Saunders, aged 48, who works at a Texaco garage on Stafford Road, said: "When we saw the traffic build up we automatically knew something had happened on the road.
"We heard from one of our customers that someone had been knocked over just outside Selco [on the Wulfrun Trading Estate].
"Police and the ambulance service arrived at the scene around 11am.
"It was shocking to see."
One worker based at a business on Stafford Road said: "There was lots of emergency services, the air ambulance was here, it was quite shocking to see."
Another worker said: "We didn't see anything, the road just went quiet and that's when we saw that [the crash scene]."
Stafford Road, going south from the island for Wolverhampton Race Course, was closed off by police.
The cordon was centred around the entrance to the Wulfrun Trading Estate.
A white lorry was situated inside the cordon.
Due to the road closure, traffic became jammed travelling on the other side of the road.
A West Midlands Ambulance Service spokesman said: "We were called at 11.04am to a man in his 50s - a pedestrian - involved in a collision with a lorry.
"A passer-by has pulled him onto the pavement.
"We sent one ambulance paramedic officer and one air ambulance from Cosford with a doctor on board.
"We assessed and treated him for potentially serious injuries before he was taken on blue lights to the major trauma centre at Queen Elizabeth Hospital."