Witnesses have spoken of the “horrendous” and “very sad” moment a young man was killed in a freak accident at a building site in Wimbledon.

The man, in his 20s, died in Cranbrook Road, off Worple Road, on Monday afternoon.

From Monday: Man killed on building site 'while working with concrete' in Cranbrook Road, Wimbledon

A spokesman for the Metropolitan Police said they were called to Cranbrook Road by the London Ambulance Service at 1.45pm after a man was “reported injured while working with concrete.”

He was pronounced dead at the scene.

Stephen Burrows, 55, from south Wimbledon, was picking up a package from the nearby Royal Mail Delivery Office at the time.

According to Mr Burrows, it appeared that a ball used to clean out concrete pumps once they have been used had become wedged in the pipe, causing a build-up of pressure that resulted in it flying out of the pump with force.

Mr Burrows, who called the ambulance, said this ball hit the young man in the head, throwing him across the road.

He said: “There was big bang. It was a huge noise, it sounded like Concord.

“This ball came flying out of this truck. It hit him straight in the head and lifted him off the ground. It was awful.

“It looked like a freak accident.

“It was instant, I’m sure he didn’t feel it.”

Mr Burrows added: “I will never forget it. It was horrendous. I will never forget it for as long as I live.”

Another witness, Rui Cruz, said he was one of the first to run to the man, and described the incident as “very sad”.

Like Mr Burrows, Mr Cruz said the death had been caused by the ball becoming stuck and then flying out of the pipe under pressure.

He added: “That ball came out like a bullet and hit him on the head, and he flew to the floor.”

The owners of the concrete supply truck, Anytime Pumping Ltd, said they were aware of the fatality but have not yet responded to requests for comment.

A spokeswoman for the Metropolitan Police said police could not comment on the cause of death until a postmortem examination had been carried out.