Ian Jackson, from Middlesbrough, had been abseiling after a climb in Chamonix, at the foot of Mont Blanc, when he fell.
He died on the way to a Geneva hospital in a rescue helicopter.
A police spokesman said Mr Jackson's two friends were watching from below as he
abseiled down the Les Gaillands rock face.
"When he was abseiling down, one of the guys made a big technical mistake and
he fell.
"When you abseil you must take two ropes and he only took one rope.
"The helicopter came but it was too late. He fell a lot of metres. He had no chance."
Mr Jackson's family have been told and are flying to France today or tomorrow.
The spokesman said the teenager's friends were "devastated" by what happened.
"They saw their friend falling from the top to the bottom. They could do nothing because when he was falling it was too late."
Les Gaillands is a crag popular with climbers in the Chamonix Valley which offers
stunning views of Mont Blanc from the top.