Several jockeys were left with broken bones and a horse was put down after a major fall at a race meeting in Port Lincoln.

Seven jockeys and horses were involved in the pile-up, which was described as one of the nastiest falls in South Australia's racing history.

The horse Harders was leading the field of 12 in the final race on Friday evening when it broke a leg and fell.

It caused a chain reaction, with six other horses and jockeys falling behind it.

Harders was being ridden by Adrian Patterson who suffered a broken collarbone, after spending the last month recovering from knee surgery after another fall.

"[I] sort of picked myself up and looked around, could see sort of jockeys just lying on the track everywhere," he said.

"It's just part of the nature of the beast - there's the highs and lows.

"Frustrating because you've just come off the back of an injury to get another injury."

Thoroughbred Racing SA's Chairman of Stewards Johan Petzer says it was the worst fall he has witnessed.

"We're very fortunate that we don't see that very often. In 23 years of stewarding that's the first time I've encountered that many horses go down at once," he said.

Jockey Simon Price considers himself lucky to have escaped with just bruised ribs, but says the accident has not put him off racing.

"We love it. You know, I think it's an adrenalin rush and I keep doing it after 25 years and I've still got the urge to do it," he said.

Several other jockeys were taken to hospital - the worst with facial fractures.