Cycling was in a state of shock on Monday after Belgian rider Wouter Weylandt died following a crash during the third stage of the Giro d'Italia.
"Despite immediate treatment there was nothing we could do," Giro doctor Giovanni Tredici told Rai Television.
"Today, our team mate and friend Wouter Weylandt passed away after a crash on the 3rd stage of the Giro d'Italia," Leopard-Trek manager Bryan Nygaard said in a statement.
"The team is left in a state of shock and sadness and we send all our thoughts and deepest condolences to the family and friends of Wouter.
"This is a difficult day for cycling and for our team, and we should all seek support and strength in the people close to us."
Leopard-Trek rider Weylandt, 26, fell off his bike in the descent from the Passo del Bocco.
Doctors at the scene cut off his helmet and performed cardiac massage for 40 minutes but their efforts were in vain despite the arrival of a helicopter.
Helmets have been mandatory in cycling since the death of Kazakhstan's Andrei Kivilev during the Paris-Nice race in 2003. Italian Thomas Casarotto died following a crash during last year's Giro del Friuli.
The last rider to die in a crash in a grand tour was Italy's Fabio Casartelli during the 1995 Tour de France.
Weylandt claimed his biggest career win when he won the same stage of last year's Giro.
"The UCI has heard of Wouter Weylandt's death with great sadness and president Part McQuaid's thoughts and prayers go to the rider's family and friends, but also to the riders, who will overcame the shock to start to race again tomorrow," the International Cycling Union said in statement.
Briton Mark Cavendish wrote on his Twitter feed: "Things like this shouldn't happen. Absolutely sick to the stomach. My thoughts are with his family. RIP Wouter Weylandt."
In 2009, riders protested against what they saw as unsafe racing conditions on the Giro after Spanish rider Pedro Horrillo narrowly escaped death in a terrible crash down a ravine.