Apprentice jockey Megan Taylor has died after falling from her horse during a race at Ashburton Raceway this afternoon.
Emergency services were called to the racecourse just after 1pm. Several other riders were involved in the collision.
St John said staff at the race meeting provided the initial assistance.
"We further responded to the incident with two ambulances and one operations manager. One patient was taken to Ashburton Hospital with moderate injuries. Two other patients with minor injuries were assessed and treated at the scene," a spokesperson said.
Karen Parsons, who trained Red Orchid, the horse Taylor was riding, said it was a terrible event, with four horses falling.
Parsons spoke with Taylor just before the race and said it would be difficult to terms with what had happened.
Four horses went down during the race, with the other jockeys receiving minor to moderate injuries, Parsons said.
A friend of the apprentice jockey said she was a beautiful soul who would be missed.
The friend said the 26-year-old was a dear friend to many people and the shock of her being taken so young was completely numbing.
The friend added she had brought energy into whatever room she walked into.
Many, including Racing Minister Kieran McAnulty, paid tribute to Taylor.
"I want to pass on my deepest sympathies to Megan's family and friends, and to all of those in the industry who worked alongside her and knew her," McAnulty said on Twitter.
New Zealand Thoroughbred Racing chief executive Bruce Sharrock said the 26-year-old's death was a tragedy.
"My thoughts are with her family and those who knew Megan very well throughout the racing community," he said.
"It's a tragic event, it's a life taken way too soon, and the industry is in mourning."
Sharrock had received an update on the others involved in the crash.
"I understand there are a few injuries but nothing of a life-threatening nature and for that we're eternally grateful."
Support services would be offered to anyone who needed them, he said.
WorkSafe has been notified and Taylor's death will be referred to the coroner.
The Racing Integrity Board will also investigate what happened.
"We'll be consulted and updated through that process as required," Sharrock said.
Ashburton Raceway did not wish to comment.