Japanese favourite Admire Rakti collapsed and died upon return to the stables after finishing last in the Melbourne Cup.

The Caulfield Cup winner was backed to start $5.50 in the $6.2 million race but tragically died only minutes after the race.

Racing Victoria chief steward Terry Bailey said an autopsy to determine the cause of death would be conducted at Werribee Vet Clinic.

Jockey Zac Purton, who won the Caulfield Cup on Admire Rakti, said he knew all was not right during the race.

"He wasn't the same horse today," Purton said.

"I got in to a nice spot, he relaxed really well, I was happy with the way the race was unfolding.

"Obviously when he didn't start towing me in to the race I knew there was something wrong with him.

"I didn't know it was as bad as it was, of course I eased him down, the horses welfare always comes first.

"He gave me a great thrill at Caulfield, for this to happen to him, it is not fair.

"I didn't think they would beat me, I thought I would win today the whole way through the run I thought I would win too.

"I didn't think they would beat me in the run."