There have been dozens of tit-for-tat shootings between warring factions in the past two years.

Mohammed Oueida, who was released from prison four months ago, was shot as he left the Coburg mosque with two other men just before 1pm on Monday.

Bullets also hit the fences of two Moore Street homes about 50 metres from the mosque.

Residents were home at the time and children were riding their bikes in the street.

As Oueida approached Nicholson Street from Moore Street, a silver BMW pulled up alongside the trio and four shots were fired from the front passenger seat, police said.

Oueida, 41, was shot once in the stomach.

He was taken to hospital by two associates ??? aged 41 and 53 ??? in a 1998 LS400 Lexus sedan.

The car used by the shooter was a BMW X5, stolen from Laura Grove, Avondale Heights, earlier that morning, police said.

Oueida, one of Australia's most influential organised crime figures when he was arrested in 2011, has been described in court as the "new Tony Mokbel".

Police describe him as highly charismatic, intelligent and influential. At the time of his arrest, police alleged he had $6 million in a Swiss bank account, a light plane, a $2.8 million mansion, a Ferrari, and suspected property and business interests in Lebanon, the Solomon Islands, Abu Dhabi and Pakistan.

Senior police had feared the release of Oueida ??? a Comanchero bikie associate with ties to Middle Eastern organised crime ??? would disrupt the delicate balance of power between warring factions in the city's north-west, the volatile epicentre of Melbourne's gun crime.

Police believe there will be reprisals, potentially escalating the brutal wrestle for control of the drug trade after key players were jailed.

And shooting the 41-year-old outside a mosque where he prayed regularly broke what little was left of an unwritten code between the factions, whose loyalties change at the drop of a hat.

"These people shoot each other over nothing, brothers shoot brothers," an underworld source said. "There is no code."

Acting Inspector Stuart Bailey called for calm, asking anyone seeking revenge to "let Victoria Police investigate it".

"It's a concern for Victoria Police that there could be some retaliatory actions taken by his victim," acting Inspector Bailey said.

"He's well-connected in the criminal fraternity so that is a concern. What we'd ask is let Victoria Police investigate it, don't take it into your own hands."

Acting Inspector Bailey said it was a targeted attack.

"We think they knew the victim was going to be in the area at the time," he said.

"There were kids riding bikes in the street and some of the rounds have penetrated a fence where people were home...It's extremely concerning for Victoria Police that we've had this and other incidences of firearm violence where members of the public have been placed a great risk."

Monday's incident adds to the growing number of shootings in public places that have put bystanders at risk.

There were two shootings in the car park of the Campbellfield shopping centre late last year that killed Kadir Ors and, in the second, injured Omar Tiba.

The Tiba shooting led to a daylight drive-by at a Glenroy tattoo parlour. His brother, Mohammed Tiba, was charged over it.

The parlour was formerly owned by Nabil Maghnie, who was shot in the head and survived last September.

But the shootings go back to April 2015, when Khaled Abouhasna was gunned down in his driveway in Altona Meadows. It remains unsolved, but police believe the target was actually his front-seat passenger, a powerful and violent drug trafficker who is now in prison and cannot be named.

Police said it was too early to say if Monday's shooting was connected to the others. Though the anti-bikie taskforce Echo is leading the investigation, it's believed they will look for a motive in Oueida's links to Middle Eastern Organised Crime, rather than current tensions between bikie clubs.

Detectives appealed for anyone with information about the shooting to come forward, particularly two men believed to be in their 20s who witnessed the incident and spoke to police at the scene, but left without providing their details.

Police also wish to hear from another man who was at the scene a short time after the incident who may have been wearing dark, full-length cultural attire.

Oueida wields such significant power that he was twice leaked sensitive police information, in 2008 and 2011, in intelligence breaches that remain unsolved.

In May 2015, while Oueida was in the Acacia Unit of Barwon Prison, he was heard speaking in code on telephone intercepts about the suspected killing or maiming of someone who owed him money, a court heard last year.

He was talking to another two other significant underworld figures, one of whom was the subject of telephone intercepts as they were being monitored while on parole.

That underworld figure - who has since been charged with an unrelated murder - had his parole cancelled after the Adult Parole Board found he had spoken to Oueida.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at crimestoppersvic.com.au.