A teenager has been left with spinal injuries after jumping off a 20ft high breakwater and landing in water just 50cm deep.

The 14-year-old girl was with pals when she ran and jumped off the east breakwater at Shoreham Harbour.

The group were videoing themselves doing the lethal “tombstoning” stunt.

Her friends watched in horror as the youngster, a pupil at Shoreham Academy, made a running jump off the breakwater only to watch her crumple as she landed feet first in the shallow water.

Witnesses dialled 999 while three of her school friends scrambled down to pull her out of the water and onto the nearby spending beach – a small area of sand and pebbles found between the harbour's east breakwater and the inner arm.

RNLI Shoreham's inshore lifeboat was scrambled at 5pm on Tuesday and arrived on the scene within minutes.

The teenager was airlifted to the Royal Sussex County Hospital in Brighton suffering spinal compression injuries and minor facial injuries.

A Coastguard spokeswoman said that last year five people were killed through tombstoning.

She said: “Our advice is simply don't do it. Don't jump from height into water when you don't know what's in the water below.

“You quite often don't know what's lurking underneath the water and you don't know what's happening with the tide.

“It could be deep but an hour later it might just be a few inches. As this incident shows people can injure themselves potentially with injuries that will affect them for the rest of their lives.”

The spokesman for Shoreham RNLI said they had already been in contact with Shoreham Academy about talking to students to warn about the dangers of tombstoning.

He said: “We did a presentation last year extolling the problems and dangers of tombstoning. We believe this girl was there when we visited and she still did it.

“We have had a word with the school and the Shoreham lifeboat crew will be going up there to re-educate youngsters.”

The group of friends who were with the 14-year-old girl were videoing their efforts - possibly to upload to the internet through websites such as YouTube and Facebook.

The two websites have countless videos of people running and jumping into water and have been criticised by safety groups for encouraging dangerous behaviour.