The 30-year-old from Mickelham died in hospital after being stabbed about 1.30am on Sunday at Chapel Street in Melbourne.
Victoria Police Detective Acting Inspector Chris Ellway said five or six people were involved in an altercation that started at one end of the street.
"We'd like them to come forward," he told reporters.
"I don't think it's a random attack but we're trying to work out what the circumstances are.
"From my information it has only lasted a short time."
A gun or imitation gun was found near the scene, and police were working to determine whether it was connected to the man's death.
Det Insp Ellway said the man was known to police and any potential links to crime groups were being explored.
He suffered several wounds from a "sharp instrument". A bottle was used in the fight but it wasn't clear if it was used to inflict the fatal injuries, he said.
The incident started on the street, he said, and wasn't linked to any venues.
No arrests have been made, with police urging any witnesses or anyone with dash cam footage to come forward.
CCTV footage from venues in the area will also be examined by investigators.
Chapel Street, a renowned dining and entertainment area, was closed between High Street and Greville Street on Sunday morning.
"It's concerning for anyone. No one wants to see violence when they come for a night out with their friends and family," Det Insp Ellway said.
In a separate incident, a woman in her 40s is fighting for life after being seriously injured during an altercation at Barwon Heads, near Geelong.
She was airlifted to hospital after the incident around 11pm on Saturday.
A 55-year-old man who suffered non-life threatening injuries has been released from hospital and will be interviewed by police.
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