He was just 34 years old.

According to Racing Victoria, thoroughbred racing's governing body in Victoria, Australia, Holland was riding in the opening race at Donald Racecourse ... when he and another jockey were thrown from their horses.

Officials say Holland was immediately tended to by medics -- and was slated to be airlifted to Melbourne -- though he ultimately succumbed to his injuries.

Racing Victoria announced the other rider who fell, and their two horses, did not sustain significant injuries in the accident.

"On behalf of the Victorian racing industry, I would like to extend our prayers and heartfelt condolences to Dean's partner Lucy, his children, his family, friends and colleagues on the incredibly sad news of his passing," Racing Victoria exec Andrew Jones said in a statement on Monday.

"It was a tragic accident at Donald today and we are all are deeply shocked and saddened that Dean has passed away as a result of injuries sustained in the fall."

Racing Victoria added an investigation into the crash is ongoing.

Holland began his racing career in South Australia in 2005 ... and piled up over 1,000 wins. In fact, he had just won a race last week.

Racing Victoria said he was the father of four children.

"Together with Racing Victoria," Victorian Jockeys Association Chief Executive Matt Hyland said Monday, "the Jockey Assistance Program will be wrapping its arms around the riding group and will be working to support Lucy and the Holland family both now and importantly into the future."