Swiss cyclist Gino Mader has died one day after crashing and falling down a ravine during a descent at the Tour de Suisse.

The 26-year-old and another rider, Magnus Sheffield of the United States, crashed on a fast downhill road approaching the end of the mountainous fifth stage into La Punt on Thursday.

"Gino lost his battle to recover from the severe injuries he sustained," his Bahrain-Victorious team said in a statement on Friday.

"Despite the best efforts of the phenomenal staff at Chur hospital, Gino couldn't make it through this, his final and biggest challenge, and at 11.30am we said goodbye to one of the shining lights of our team.

"Our entire team is devastated by this tragic accident, and our thoughts and prayers are with Gino's family and loved ones during this incredibly difficult time."

Medical staff who reached Mader found him motionless in water. They performed CPR before he was airlifted to the hospital.

Organisers said they were clarifying how the accident happened.

The Tour de Suisse is a preparation race ahead of next month's Tour de France.

Mader's death was announced about 30 minutes before the scheduled start of the sixth stage in the eight-day race. The start was delayed.

"We are heartbroken," Tour de Suisse organisers said in a statement.

"Gino, you've been an excellent rider but even more a wonderful person. Always smiling and making people happy around you."

The stage five route was criticised by world champion Remco Evenepoel, who finished 10th and is fourth overall.

"While a summit finish would have been perfectly possible, it wasn't a good decision to let us finish down this dangerous descent," Evenepoel wrote on his Twitter account.

"As riders, we should also think about the risks we take going down a mountain."

Sheffield sustained a concussion and bruises and was treated at a local hospital, organisers said.

Mader placed fifth in the Spanish Vuelta in 2021 and also was fifth in the Paris-Nice stage race in March.

Denmark's Mattias Skjelmose leads the general classification standings from Austrian Felix Gall.