Playing Icarus as they leap off sheer cliffs and fly at eye-watering speeds along mountainsides, thrill-seekers dressed like flamboyant bats have become an increasingly common sight in the Alps. But the incredible rush of wingsuits can come at the ultimate price.

On a plateau of the Brevent mountain in Chamonix, France, a group of men and women in winged bodysuits are lined up along the edge of a sheer cliff face, facing the snowy peaks of Mont Blanc and staring down at a 2,500-metre (8,300-foot) drop.

Suddenly, they throw themselves off, drawing gasps from nearby tourists.

Their flight lasts barely a minute. Within eight seconds, they are up to speeds of 200 kilometres per hour (120 miles per hour).

They fly "by pushing against the air: it's gravity that creates the magic of it all, the wind doesn't do anything," said Roch Malnuit, head of the French Base Association.

First tested by wingsuiters in June 2012, Brevent has quickly become a renowned port of call for the discipline, along with Lauterbrunnen in Switzerland.

Its fame spread as a result of Internet videos and within weeks there were 30 or so jumps a day.

But then came the first injuries, and then the first death, and the authorities in Chamonix shut the sport down there for a year before reconsidering their decision.

"They only speak about us when there are accidents," said Swiss wingsuit enthusiast Geraldine Fasnacht, 28. She was the first to jump from the 4,500-metre high Matterhorn in Switzerland last June. "It's a magnificent sport that requires an enormous amount of preparation and work."

- A dangerous encouragement? -

The role of video in the sport remains controversial.

Films of particularly daring stunts have become Internet sensations, as expert wingsuiters skim perilously close to mountainsides and push themselves towards the record flying speed of 363 kph.

"It's not the practice itself that is the problem -- it's the way it is mediatised," said Colonel Blaise Agresti, mountaineering adviser to the police.

"It gives ideas to people with little experience, and leads to competition for the most sensational images. The game is to get as close as possible to the ground."

Frenchman Loic Jean Albert became a star of the sport in 2003 by flying just three metres from the side of a snowy slope he hurtled down in Switzerland.

"Today we see this all the time. The problem is that some do it without any experience. When they fly just two or three metres off the ground, there is no margin for error," said Jean-Philippe Gady, president of the French Association of Paraclimbing.

The Base Jumping Fatality List, published on Blinc Magazine's website, says there were 21 wingsuit deaths worldwide in 2013.

There are thought to be around 2,000 practitioners -- most of them in the United States and Australia. There are no tests or diplomas in wingsuiting, although schools in Norway, Austria and the US do offer courses.

"What we recommend is to get insurance and do around 200 jumps from a plane, to get a mastery of the air, before jumping off a cliff," said Malnuit.

Gady jumps as many as 180 times a year. "With rates like that, we can afford do try technical jumps," he said.

Filming with GoPro cameras fixed to his helmet, he has produced films that are almost too tense to watch as he flies through narrow corridors or under a footbridge among the peaks of Mont Blanc.

- Makes it look easy -

"Video has a positive side," said Vincent Descols, one of the first to jump from Brevent. "It allows us to fine-tune the art of flight: the accuracy, the height at which to open the parachute.

"But other videos are a problem because they give the impression that it's easy," he added, saying there were a lot of dangerous egos involved in the sport.

The death in August 2013 of Briton Mark Sutton, the James Bond parachutist from the London Olympics, followed by that of three young wingsuiters in Switzerland during filming for extreme sports channel Epic TV in March, has reignited the debate over the way films encourage risk-taking.

"We had a moment of doubt after the death of Dan, Brian and Ludo because we got a lot of criticism," admits Jools Benker, head of wingsuiting at Epic TV. "But they are the ones taking the risks, they understand them. The fact they are being paid does not push them to fly closer to the ground."

The channel, based in Chamonix, claims to have 2.7 million visitors to its site each month, primarily Americans, Brits and French. The videos are a hit, though they bring in little revenue to this start-up of 35 employees which struggles to sell their footage on to outside companies who remain cautious.

Jean-Noel Itzstein, a pioneer of wingsuiting, regrets the bad reputation: "People think we're committing suicide by jumping. But in mountaineering, there are lots of deaths every year and it's accepted."