Police are investigating a potentially deadly booby trap that left a Canterbury teenager with a slashed throat.

David Watson, 14, and two friends were biking down a dirt track in Diamond Harbour, near Lyttelton, about 12.45pm on Monday when he was thrown off his bike after riding into the trap set up in the trees.

Strong gardening string had been pulled tightly and zigzagged three times across the track and tied to trees.

Sergeant Phil Newton, of Lyttelton police, said David was hit at throat level.

“If the string had needed a few more pounds pressure to break, then we could have been looking at something far more serious here,” he said.

Constable Nick Jack said police thought it was a prank gone wrong, set up by other children.

“We can’t rule out someone older has done it, but given the location (a popular short-cut with kids) it’s doubtful.”

David’s mother, Michelle Watson, was angry at the “viciousness” of the prank.

She said the trap was made from very thin dark green garden string and her son never saw it.

There were suspicions that another group of boys who were well known in the community and to police could have been responsible.

Mrs Watson said her son went straight home after the incident.

“I think he was in shock. He said `Some idiot has put this string across and I’ve come off my bike’.

“I was absolutely horrified and my first reaction was that he could have cut a major artery, he could have broken his neck if the string hadn’t broken.”

Although David had suffered a cut and burn on his neck he did not need medical treatment.