Homicide detectives are working to gather evidence after a man's body was found by a passer-by in a car park in Melbourne's east.

The man, believed to be in his 30s, was found off Rollings Road in Upper Ferntree Gully on Saturday at about 3pm, Victoria Police said.

"The exact cause of death is yet to be determined but it's being treated as suspicious at this stage," a police spokeswoman said.

The man's body was found by a passer-by. (9NEWS)

The death is being treated as suspicious. (9NEWS)

An Ambulance Victoria spokesman said paramedics tried to resuscitate the man at the scene but were unsuccessful.

Witnesses described hearing a car breaking loudly before the body was discovered.

"I did hear screeched breaks, which wasn't unusual for this area," one woman told 9NEWS.

"I'm shocked, nothing like this has ever happened around here before. Car accidents... but not bodies lying around."

A murder probe has been established with the homicide squad investigating.