Animals rights activists are up in arms over the unexpected deaths of two horses at the Melbourne Cup and have called for immediate changes within the racing industry to prevent any more unnecessary deaths.

Recent Caulfield Cup winning horse Admire Rakti, went into the Melbourne Cup as the favourite but died after collapsing back at the stalls just five minutes after finishing in last place. Araldo, who placed seventh in the Cup, was euthanased on Tuesday night after breaking his leg.

The Coalition for the Protection of Racehorses has orchestrated a campaign over the past few weeks in a bid to raise awareness of an industry "rife with welfare problems".

About 40 of its members protested at Flemington in the aftermath of race seven with one of the members capturing the moment Admire Rakti collapsed in the stalls on video.

"We're very distraught by the news that two horses lost their lives," the group's director Ward Young said.

Mr Young said 129 horses died on Australian race tracks between August last year and July this year - one horse every 2.9 days - and he called for the banning of the whip and two-year-old racing.

"Their joints and muscles aren't fully formed. While not many of them break down as two-year-olds, a lot of them break down in the following year and more than half of those horses who died were raced as two-year-olds," he said.

"We question the racing industry's credentials on horse welfare and safety, we only have to look at jumps racing. Horses die in that and they keep allowing that to continue."

The group launched its 'Horse Racing Kills Campaign' with a 22-metre billboard in Melbourne with the question: "Is the party really worth it?" accompanying an image of a dead horse

Mr Young said he believed the deaths of both horses would change people's perspectives on the treatment of race horses.

Racing Victoria described the death as "very rare" and have offered their condolences to the horse's owner Riichi Kondo and trainer Tomoyuki Umeda.

"The exact cause of death is yet to be determined, although the circumstances of the horse's passing are very rare," Dr Brian Stewart, Racing Victoria's Head of Veterinary and Equine Welfare, said in a statement. "A post mortem will be conducted at the University of Melbourne Veterinary Hospital as is standard practice."

Admire Rakti, which won the Caulfield Cup in brilliant style last month, raced near the lead for most of the 3200-metre journey.

As he rounded the final bend, the horse was clearly under pressure and dropped back through the field sharply.

He finished 25 lengths behind the second-last horse.

Admire Rakti carried the hopes of Melbourne Cup punters as the $5.50 favourite.

Racing Victoria chief steward Terry Bailey said the seven-year-old collapsed and died when he returned to the tie-up stalls after the race.

Racing Victoria vets will conduct an autopsy.

"It's a shame. We had such a nice, clean-run Melbourne Cup," Bailey said.

There was an overwhelming reaction on social media, with thousands of people tweeting their horror and sadness at Admire Rakti's death.

Apart from the odd racing pundit, very little support was being thrown behind the racing industry. 

I heard next year the #MelbourneCup favorite will be "any horse to die", probably paying $1.04 #HorseRacingKills — Danial Pearce (@tigris666) November 4, 2014

What a debacle horse racing really is. I am horrified about the death and casualty of two horses. Hope it was worth it. #melbournecup — alive3d (@alive_3d) November 4, 2014

If only it was the nation that stopped the race. #melbournecup #horseracingkills — lucy donnelly (@thereallucyd) November 4, 2014

If human track and field racing had the same death toll as horseracing, would we allow it? — Dominic Knight (@domknight) November 4, 2014

Admire Rakti is a tragedy but don't make knee jerk reactions on something you don't know a lot about. Research and understand. #melbournecup — Dale Roberts (@ozdale) November 4, 2014

Surely we can continue the Melbourne Cup tradition without the cruelty of racing horses to death? Conflicted as to where I stand on this. — Elias Jahshan (@Elias_Jahshan) November 4, 2014

#MelbourneCup get a life & cry for the starving children, not the death of a champion race horse — Oliver Renfrew (@OliverRenfrew) November 4, 2014

- with Tammy Mills.