New Zealand Thoroughbred Racing has launched an investigation into the deaths of three horses at Auckland's Ellerslie Racecourse on Monday.
Two were euthanised after falling and injuring themselves in hurdle races, another after it was injured in the steeple chase.
Thoroughbred Racing general manager of racing and handicapping Matthew Hall said it was not normal for three horses to die in one race day.
"We've immediately launched an investigation into how the deaths have occurred, and we'll be doing everything we can to ensure any safety improvements required are made."
A racing expert agreed it was unusual to have so many horses die in a single race day.