A 21-year-old Swiss snowboarding champion died in an avalanche on Tuesday after a slab of snow broke away during a film shoot in Switzerland and swept her down a narrow, rocky slope.

Estelle Balet, who won the Freeride World Tour in 2015 and 2016, died in the one km long avalanche above the Swiss village of Orsières despite efforts of emergency crews to save her, police in the canton of Valais said in a statement.

Last year, Balet became the youngest champion of the Freeride World Tour, in which skiers and snowboarders compete by riding down steep, often-rocky ungroomed slopes. Events are sometimes halted due to avalanches, including last February at a competition in Austria.

Police said Balet was the second person to ride down the slope on Tuesday during filming.

She had been freed from the avalanche by the time emergency crews arrived. "Despite immediate efforts to revive her, she died at the scene," police said. "An investigation has been started to determine the causes of the accident."

Balet, who is sponsored by the Swiss watchmaker Swatch, had been wearing a device meant to help locate people in avalanches, as well as a helmet and an airbag designed to increase the chances of surviving a snow slide.