Two horses died after a head-on collision during an early morning training run at Del Mar track in California, officials said Thursday, sparking calls for an investigation by state regulators.
Del Mar Thoroughbred Club spokesman Dan Smith said the two horses, three-year-old Carson Valley and two-year-old Charge a Bunch were killed after colliding at around 6:30am.
The accident occurred when Charge a Bunch threw its jockey Giovanni Franco and bolted back down the track in the wrong direction.
The horse then collided with Carson Valley, trained by legendary US trainer Bob Baffert, who was heading up the track.
Carson Valley's rider Assael Espinoza was hospitalised complaining of lower back pain. Franco was uninjured in the collision.
Triple Crown-winning trainer Baffert described the incident as a "freak accident".
"This was a very unfortunate accident and it is a shock to everyone in the barn," Baffert said in a statement.
"We work every day to take the best care of our horses, but sometimes freak accidents occur that are beyond anyone's ability to control."
The accident comes with horse racing in California facing scrutiny following a spate of equine deaths at the famed Santa Anita racetrack outside Los Angeles.
Thirty horses died at the course in the space of six months, prompting California Governor Gavin Newsom to give his backing to legislation which would give local authorities greater power to suspend horse racing licenses.
Animal rights activists have also slammed the high death toll, calling for an outright ban on horse racing.
On Thursday, People for the Ethical Treatment of Animals (PETA) said the fatalities at Del Mar should be fully investigated by the California Horse Racing Board.
"PETA requests that Del Mar and all other California racetracks release records of horses who have gotten loose on the tracks and urges the California Horse Racing Board to launch a full investigation in order to eliminate the dangers of training," PETA senior vice president Kathy Guillermo said.
"If racing can’t be done without horses dying, it shouldn't be done at all."