Images from a helmet camera may reveal what went wrong when two men wearing wingsuits and attempting an illegal cliff jump at Yosemite National Park in the US crashed to their deaths, a park official says.

Video of the deadly stunt from a GoPro camera mounted on the helmet of renowned climber Dean Potter shows his friend Graham Hunt hit the ridge first, said Mike Gauthier, the park's chief of staff. He said Potter swooped left, possibly trying to avoid his partner, but hitting the rocks a split second later.

"It could have been an evasive maneuover," Gauthier told the San Francisco Chronicle in a Tuesday report. "Someone else said they saw a clipped piece of a tree up there, so we don't know for sure."

Dean Potter was one of two men killed in a BASE-jumping accident at California's Yosemite National Park.

The two men jumped at dusk on Saturday from Taft Point, 3500 feet (1066 metres) above the valley floor. They wore batlike suits designed to glide them downward at 160 k/hr from the cliff face, through rocky outcroppings and over trees to a safe landing. Instead, they died instantly, and their bodies were found 50 metres apart.

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*Extreme climber Dean Potter dies in Yosemite BASE jumping accident

Park officials are using video from the camera mounted on Potter's helmet and other still photo images taken by observers to re-create the accident, the newspaper reported. Potter's girlfriend, Jenn Rapp, shot video of the launch and heard two impact sounds, Gauthier said.

Potter, 43, and Hunt, 29, were both experienced in the extreme sport of wingsuit flying, a more dangerous offshoot of Base jumping - parachuting off buildings, antennas, spans such as bridges and Earth. It is illegal in all US national parks, and jumpers who are caught are fined and have their equipment confiscated.

Dean Potter's death may have been captured on video, investigators say.

At least five people have died in Base jumping accidents in US national parks since January 2014, including the most recent deaths at Yosemite, said Jeffrey Olson, a National Park Service spokesman. The deaths of Potter and Hunt remain under investigation.

"In this sport you have a fraction of a second to make a life-or-death decision," said Tom Evans, a Yosemite photographer, who writes about rock climbing. "Just one instant of inattention is all you need."