What was supposed to be a thrilling ride down a ski slope inside a giant inflatable ball ended in tragedy for the two Russian men inside.

One died and the other was badly injured on Jan. 3, when the transparent plastic ball called a zorb veered off course and sailed over a precipice in the rugged Caucasus Mountains of southern Russia.

The man who died, 27-year-old Denis Burakov, was with friends at the Dombai ski resort, where they frequently went snowboarding, when he decided to take a ride in a zorb being operated next to a beginners' slope.

His friend Vladimir Shcherbakov joined him.

An eight-minute video taken on Burakov's phone by one of his friends showed the two men being fitted into harnesses inside the zorb, which consists of two polyurethane balls with a layer of air between them.

The zorb was then released to roll down the hill, the two men spinning inside.

But the zorb bounced off of the intended path, and a man waiting for it at the bottom of the hill tried in vain to catch the ball before it popped over a rocky ledge and disappeared down a gorge below Mount Mussa-Achitara, as Burakov's friends watched in horror.

Fell into gorge

Vasily Akimenko also witnessed the accident and recorded the video showing the zorb spiralling down the gorge.

"Two skiers went down, but only one could get there, because it was so difficult to get down," Akimenko told the Associated Press in an interview conducted via Skype.

"It seems to me there was an abyss down there," Akimenko said.

The Emergencies Ministry said both men were ejected from the zorb as it tumbled and they landed on the snow about 10 metres apart.

They were rescued by two skiers, who then pulled both men up to the top of the hill.

Burakov suffered serious spinal injuries and died on the way to the hospital.

Shcherbakov suffered a concussion and other injuries and remains hospitalized.

The accident prompted the emergencies minister to demand on Wednesday that Russia address its lax enforcement of safety rules for winter sports, citing a series of accidents over the January holidays.

Violated safety rules

Sergei Loginov, deputy director of Z-orb.ru, the largest supplier of zorbs in Russia, said the zorbing run that killed Burakov was conducted in violation of all safety rules.

Zorbing requires a groomed gentle slope with fences on both sides of the track and a secure spot at the bottom where the ball can be safely brought to rest, he said, but none of this was present at Dombai.

"It's not even irresponsibility. It's an experiment on life," Loginov said. "It's all or nothing. They either survive or they don't."

The sport of zorbing originated in the 1990s in New Zealand and is now done around the world, most often on grassy slopes.