Homicide detectives are investigating the stabbing death of a man in the inner Melbourne suburb of Fitzroy.

Mystery still surrounds the death of the 21-year-old Werribee man, who died after being stabbed multiple times.

Police have blocked traffic on Johnston Street, Fitzroy. Credit:Ben Millar

He was discovered in Johnston Street by a council worker about 5am. He collapsed soon after and was dead before the ambulance arrived.

A nearby convenience store worker said his colleague had heard screaming from near the corner of Johnston and Fitzroy Streets around the time of the incident.