An exercise rider and the horse he was riding are dead after what one rider described as a "freak accident" at Toronto's Woodbine Racetrack this morning.

Just after 6 a.m. ET, Mourad Boudraa, 42, was riding filly Tawney's Wish in a training area on the south side of the racetrack property northwest of the city when the horse had a medical issue, possibly a heart attack.

The trainer, an experienced rider originally from Morocco, was crushed into the track railing and then by the weight of the horse as it collapsed.

"Horror, absolute horror," Trisha Greer, owner of Tawney's Wish, told CBC News. "It's one thing to lose a horse, but when you lose the rider too, that's just traumatic."

Emergency services personnel were called to the sand track area, where they found Boudraa trapped under the dead horse. Boudraa was pronounced dead at the scene.

Woodbine 'deeply saddened'

Shawn St. Pierre, an exercise rider with 32 years of experience, told CBC News such incidents are rare. 

"It is a freak accident. It doesn't happen often, but it does happen," he said.

It was earlier reported that a jockey had died, and then police later said the dead man was a trainer. CBC News has since confirmed that Boudraa was an exercise rider.

A statement issued by Woodbine says, "All of us in the Woodbine community are deeply saddened by the death of exercise rider, Mourad Boudraa, in this morning's tragic accident. Our thoughts are with his family."

"We are working closely with officials to support them in their investigation," said Jamie Martin, executive vice-president, racing, for Woodbine Entertainment Group. "Our hearts and sympathies go out to Mourad Boudraa's loved ones in this sad and very difficult time."

Boudraa and his wife live in Toronto and he has family in Morocco.

Toronto police have taped off a large area at the rear of the property where the track's barns and training area are located.

Ontario's Labour Ministry will investigate. The horse, who had one start this year and $368 in winnings, is being transported to Guelph, Ont., where the body will be examined.

Mike Pownall, an equine veterinarian, said the horse's cause of death won't be known until a necropsy is performed.

"It's like when you find those athletes that suddenly die and you find there's a heart defect, that would be the human
equivalency," Pownall said. "You have no idea it was existing, or you could prevent it, or you could do anything to alter the course."

In 2011, Canadian Olympic champion Eric Lamaze was riding his horse Hickstead in Italy when the animal suddenly collapsed and died of an acute aortic rupture. The horse had carried Lamaze to gold and silver at the Beijing Olympics in show jumping. 

The Ontario Racing Commission, which requires a necropsy whenever a racehorse dies, collects information for a database on common racehorse injuries in the hopes of minimizing future problems, Pownall said.