JOHANNESBURG -- Burry Stander, a two-time Olympian from South Africa and one of the world's best mountain bikers, was killed while training Thursday when his bike collided with a taxi. He was 25.

The circumstances of the accident near his home in Shelley Beach, south of Durban, were still being investigated, Cycling South Africa said.

Stander competed at the 2008 and 2012 Olympics, finishing fifth at the London Games. He was a former under-19 and under-23 world champion.

"I'm totally shattered," said Gideon Sam, president of the South African Sports Confederation and Olympic Committee. He called Stander "talented, ultra-competitive but at the same time extremely humble and a true gentleman."

Stander's death prompted a flood of tributes on social media from South African athletes, politicians and celebrities. Oscar Pistorius, the double-amputee Olympic runner and multiple Paralympic medalist, said on Twitter he was "utterly devastated."

"A South African Icon and sporting great. RIP my friend," Pistorius wrote.

Cycling South Africa said Stander was the country's most successful mountain biker and "a true icon and sporting role model."

Stander won South Africa's Cape Epic stage race with Swiss teammate Christoph Sauser in 2011 and the pair successfully defended their title in 2012.

"Never felt so empty since my dad passed away when I was a kid. @africanmtbkid I will never forget you," Sauser posted on Twitter, using Stander's Twitter name.

Stander was the second leading cyclist to be killed in a road accident in South Africa in recent years. Carla Swart died in January 2011 when she was hit by a truck while training.