Dutch cyclist Annemiek van Vleuten entered intensive care after suffering three cracked vertebrae in a stomach-churning high-speed crash during the Olympic road race on Sunday.

The 33-year-old was leading the race and 10km from Olympic gold when she tumbled over her handlebars on a tricky descent, leaving her motionless in a heap on the side of the road.

The Dutch Cycling Federation initially said she was conscious and had been taken to hospital.

"Heavy concussion and three small fractures in her lumbar spine. She continues 24 hours in i.c. (intensive care)," the federation later added on Twitter.

But the federation added that she was "conscious and speaking".

TV images of the crash made for uncomfortable viewing as Van Vleuten was left sprawled on the side of the road when victory in the 137km race seemed within her grasp.

Her Dutch team-mate Anna van der Breggen won the race but then spoke of her shock at riding past her stricken team-mate.

"It really shook me when I saw Annemiek crashed in the road," said the new champion.

"Annemiek was leading but I realised I was now first in the team. I was shocked."

Sweden's Emma Johansson took second and also spoke of her concern for Van Vleuten.

"Annemiek's crash was horrendous. We just want to know she is OK," she said.

Van Vleuten skidded on a sharp right-hand bend and flipped forward over her handlebars, plunging head-first into the road and kerb.

The crash happened on the Vista Chinesa, the same descent where the leaders of the men's race wiped out on Saturday with Italy's Vincenzo Nibali suffering a broken collarbone and Colombia's Sergio Henao breaking his pelvis.

Australia's Richie Porte broke a shoulder blade on the same section of the course during the penultimate descent on Saturday.