Caulfield Cup winner Admire Rakti has collapsed and died in its stall after finishing last in the Melbourne Cup.

And in a tragic postscript to the Cup, seventh-placed Araldo was put down hours after the race following an incident on its way back to the mounting yard where it fractured its leg after kicking a fence.

Admire Rakti was the heavily-backed pre-race favourite, and raced near the lead but faded in the final 400m as German runner Protectionist went on to win the Cup.

Reports emerged soon after the race that the Japanese horse had collapsed in its stall, with Racing Victoria chief steward Terry Bailey confirming afterwards that it had died.

In a statement, Racing Victoria's head of veterinary and equine welfare Dr Brian Stewart expressed his sympathies to Admire Rakti's owner and trainer.

"It is with sadness that we confirm that Admire Rakti has passed away in his stall following the running of the Melbourne Cup," Stewart said.

"The exact cause of death is yet to be determined, although the circumstances of the horse's passing are very rare.

"A post-mortem will be conducted at the University of Melbourne Veterinary Hospital as is standard practice.

"Our sympathies are extended at this time to the owner Mr Kondo, trainer Mr Umeda and his staff who cared deeply for their horse and are naturally saddened by their tragic loss."

Admire Rakti's owner Riichi Kondo walks through the stables after the pre-race favourite died. ( AAP: Tracey Nearmy )

The jockey riding Admire Rakti, Zac Purton, said he could tell something was wrong with the horse early in the race and made precautions to try and protect its welfare.

"I knew he was in trouble when he didn't tow me into the race around halfway from home," Purton said.

"So I eased him down straight away, the horse's welfare comes first.

"It's very sad. He gave me a great thrill at Caulfield and for this to happen to him is just not fair.

"I didn't think they'd beat me. I thought he'd win today and the whole way through the first half of the race I thought that too."

The death of Admire Rakti follows the death of Verema, who broke the cannon bone in her near foreleg during the 2013 Melbourne Cup and was put down.

Araldo euthanased after breaking leg post-race

Araldo runs during a trackwork session at Flemington Racecourse. ( Getty Images: Vince Caligiuri )

Meanwhile, the Mike Moroney-trained Araldo, which finished seventh, was put down hours after it took fright on the way back to the mounting yard and broke its leg on a fence.

Araldo leapt forward after a flag was waved in its face, jumping a steel rail and getting its leg caught in a barrier.

While trying to jerk its leg free, it is believed it fractured its pastern in the process.

The horse was rushed to Werribee Veterinary Hospital, but experts concluded the injuries sustained were too severe to recover from.

Racing Victoria's head of veterinary and equine welfare Dr Brian Stewart issued a statement confirming the news and expressing sympathy to the horse's connections.

"It is with sadness that we confirm that Araldo has had to be humanely euthanised as a result of the injury it suffered in a freak accident following the Emirates Melbourne Cup," Dr Stewart said.

"The horse received immediate veterinary care and was transported to the University of Melbourne Veterinary Hospital, however, sadly the fracture in its pastern was not repairable.

"The owners made the decision to humanely euthanise Araldo in the best interests of the horse.

"Our sympathies are extended at this time to trainer Mike Moroney, his staff and the owners who are extremely saddened by the loss of their horse in such tragic circumstances."

Animal protection groups speak out

The RSPCA released a statement on Tuesday afternoon saying the tragic events were a "stark reminder" of the damage the sport can have on horses.

"Sadly, injury and death are the price some horses pay for our entertainment in a sport that puts intense pressure on animals to perform to the limits of their endurance," the statement read.

"Events like these are a stark reminder to the community of the real risks to horses associated with racing.

"This is a tragic outcome for both horses and we expect there to be a full and transparent investigation undertaken into both incidents."

The Coalition for the Protection of Racehorses (CPR) followed suit, saying the incidents today are anything bat rare occurrences in the world of horse racing.

"This is a sport that has been doing what it wanted to do for the last 200 years, and now it's starting to realise that it needs to make some changes," CPR campaign director Elio Celotto said.

"How common is what we saw today? Well, we do know that 125 horses have been killed in the last 12 months, and that's roughly one horse killed every three days.

"We think that the pressure we're applying to the racing industry, exposing the dark side of the industry, is going to force them to make these changes."