Jonas Vingegaard has been taken to hospital along with leading Australian rider Jay Vine after some of the world's best cyclists suffered injuries in a mass crash at high speed in the Itzulia Basque Country race in Spain. 

The reigning double Tour de France champion Vingegaard was reported to have suffered a broken collarbone and several broken ribs but was "conscious" after the alarming crash that threatens his hopes of a famous treble in July.

Vine, last year's Tour Down Under winner, also ended up crashing heavily in a concrete ditch and was taken away by ambulance.

The 28-year-old was later diagnosed with a fractured cervical vertebra and two fractures in his thoracic spine, with no other major injuries or head trauma. 

It was a disastrous day for another modern-day great too, with Remco Evenepoel, the 2022 world champion, managing to walk away from the crash despite suffering what his Soudal-Quick Step later confirmed was a fracture to his right collarbone and to his right shoulder blade.

He will need surgery on Friday in Belgium.

Giro d'Italia champ Primoz Roglic, who had been the overnight leader, also abandoned the race after giving a thumbs-up to cameras from the team car to show he was OK.

In all, 12 riders near the front of the peloton were involved in the crash, which happened with about 35 kilometres left of the fourth stage between Etxarri Aranatz and Legutio, in northern Spain.

The leaders were making a sweeping right-hand turn on a slight but swift descent, with some sliding off, sending others off the road into the ditch.

Denmark's Vingegaard, who has been in spectacular form and was favourite for the 2024 Tour de France, had to be carried to the ambulance in a neck brace and needed oxygen after treatment at roadside by doctors.

The race was then neutralised until the finish, with only the six riders who had been at the front being allowed to sprint for the finish to try to win the stage, with victory eventually going to the underwhelmed South African Louis Meintjes, who admitted it was a hollow triumph.

"It's a sad day. I wish all the guys who crashed all the best and wish them a fast recovery," Mattias Skjelmose, who took the overall race lead from Roglic, said at the finish.

"My mind is with the guys who crashed, and right now I am not thinking about the leader's jersey."

The crash, which featured three of the world's most outstanding riders in Vingegaard, Evenepoel and Roglic, was also a huge blow for 25-year-old Vine, who has graduated from riding a turbo trainer in his living room to being a peloton star.

He had begun the week-long race on Monday with an exceptional time trial that had left him second behind only Roglic at that stage and revealed afterwards that the Itzulia had been only a late addition to his schedule.

Earlier on Thursday, Roglic's teammate at BORA-Hansgrohe, Lennard Kamna, was reported to be in a "stable condition" in intensive care after he had collided with a car during a training ride in Tenerife.

AAP