Mystery surrounds the death of a young man who was stabbed multiple times in inner Melbourne.

A passing council worker found the man in distress in Fitzroy about 5am Sunday (AEDT), police said.

The worker gave the man first aid and called 000 but paramedics were unable to revive the young man.

Detective Sergeant Allan Birch said police are still trying to establish what happened to the man.

"It would appear he had a number of stabbing injuries," he told reporters.

"We don't know what happened ... we don't know exactly how the injuries were inflicted."

Police were initially unable to identify the man, but now say he is a 21-year-old from Werribee.

The man was found in Johnston Street near the intersection of Fitzroy Street.

On Sunday morning a small lane way was draped with a tarpaulin as crime scene examiners combed the area.

Det Sgt Birch said police are not aware of any witnesses besides the council worker and urge people with information to come forward.

He said the homicide investigation is very wide, given the lack of information.