Officers from the Metropolitan Fire Brigade discovered the badly burnt body at Alma Park in St Kilda East after receiving a report of a fire at 6.18am on Monday.

Police found a backpack and a container of accelerant near the body, which lay on a grass embankment about 200 metres from a railway bridge on Alma Road.

Police spokeswoman Creina O'Grady said police did not believe the man was electrocuted.

Senior Sergeant Hans Harm said a man in the park called authorities to report a fire in the bushes.

"The gentleman who called it in didn't know what it was," he said. "That's probably a good thing. It's certainly distressing."

Police shielded the body from view and diverted workers and school children who normally walk through the park.

A cyclist, who would not give his name, said the area was popular for "train surfing" and there had been two other deaths from the practice at the same location.

Police would not comment on the possibility of the man being a train surfer or vandal, but said the accelerant found nearby was not spray paint.

Trains were suspended between Elsternwick and South Yarra through the morning, but services resumed before midday.

A report is being prepared for the coroner.

With Rania Spooner

For help or information visit beyondblue.org.au, phone Suicide Helpline Victoria on 1300 651 251, or Lifeline on 131 114.