American favorite Connor Fields crashed heavily in the third run of his semi-final in the Olympic men's BMX race on Friday and was taken off the track on a stretcher and loaded into an ambulance.

There was no immediate word on his condition.

Fields had looked in total control as he finished third and first in the first two runs of his semi-final heat. ut in the third run he appeared to make contact with another rider going into the first steeply-banked 180 degree turn on the snaking concrete course and pitched forward. He was treated by medical staff before being taken away.

The reigning champion had already done enough to qualify for the final later, but his hopes of a second successive gold medal look over.

“We can confirm that Connor Fields is awake, stable, and awaiting further medical evaluation," said U.S. Olympic and Paralympic Committee chief medical officer Dr. Jon Finnoff in a statement. "He will remain in the hospital under observation."

It was the worst of several crashes, one of which also saw Australian rider Saya Sakakibara also require treatment although she was not badly hurt.

American Alise Willoughby, second in Rio and Dutchwoman Laura Smulders, were also involved in heavy crashes and failed to make the final of the women's race.

Fields was awake following the crash and awaiting further medical evaluation.

NBC Olympics contributed to this Reuters report.