Race horse Regal Monarch has been euthanised after falling in race four at Flemington on Melbourne Cup day.

Regal Monarch, the horse that fell during race four on Melbourne Cup day, has been euthanised.

The horse was taken to Werribee Veterinary Hospital after the fall at Flemington on Tuesday, but could not be saved, said Racing Victoria's chief vet Grace Forbes said.

"It is with sadness that we can confirm that the horse has been humanely euthanised on veterinary advice as a result of the injuries sustained," she said.

"Our sympathies are extended at this time to the owners of Regal Monarch, trainer Chris Waller, and his staff who cared deeply for their horse and are naturally devastated by their loss."

Jockey Joao Moreira was cleared of serious injury but was unable to ride in the main race.

Activist groups including the People for the Ethical Treatment of Animals and the Coalition for the Protection of Racehorses are outraged, demanding reforms in the industry.

"It's time for the racing industry to ban the whip and phase out 2-year-old racing so that racehorses aren't overworked and over-exerted," Coalition for the Protection of Racehorses campiagn director Elio Celotto said in a statement.