Underworld boss Bilal Hamze was killed in a “brutal, execution-style murder” in Sydney’s CBD on Thursday night, NSW Police say.

Mr Hamze, 34, was the cousin of notorious Brothers 4 Life gang leader and murderer Bassam Hamzy, who is locked up in Goulburn Supermax Jail.

Detective Superintendent Danny Doherty said paramedics were called to Bridge Street near Circular Quay late on Thursday in response to a drive-by shooting.

“Police were told a number of shots were fired by a person or persons, more than one person anyway, who was passing in a black vehicle that left the area,” he said.

“Detectives are conducting an extensive canvass of the area, and that is involving not only talking to any witnesses or potential witnesses but also looking for CCTV, anyone with mobile phone footage or dashcam footage.

“This was a brutal, execution style murder and it was carried out in a busy street in the middle of Sydney CBD.”

Detective Superintendent Doherty said it was “extremely fortunate” that passers-by weren’t injured.

“Detectives will now explore a number of inquiries, including ongoing conflict between rival families and organised crime networks.”

Forensic and ballistic examinations of the scene continued late into Friday morning.

A second crime scene has been established in the Lane Cove area, where a burnt-out vehicle was found shortly after the shooting.

Homicide squad detectives will investigate, alongside the criminal group squad, Strike Force Raptor and Central region police.

‘Is that a gun?’: Witness

A witness said she was in bed reading when she heard the shots, followed by an eerie silence.

“All of a sudden I heard several shots go off three, four or five and I was like, ‘Is that a gun?’,” the US citizen said.

“I didn’t hear any cars or anything for at least a minute or two and I thought that I should go outside and look … then I heard sirens, probably a few minutes later.”

The woman said being from America, where firearms were much more common, she was shocked it was a shooting.

“I didn’t think it was [guns] because I’m in Australia … that’s wild, knowing that I live just a walk from here.”

NSW Police said a short time later, a burnt-out vehicle was discovered at Fleming Street in Northwood, on Sydney’s north shore, where officers had established a second crime scene.

Forensic teams remained at the scene at Bridge Street, with officers examining bullet holes on the side of the building.

A black jacket was seen being placed into an evidence bag.

Detectives are concerned about possible reprisal attacks because of the high-profile nature of the shooting.

Police remained on the scene of the shooting late into Friday morning. Photo: AAP

Mr Hamze is the son of Maha Hamze, the family’s matriarch, who was shot and seriously injured outside her Auburn home in 2013.

That same townhouse was targeted in October when another cousin, Mejid Hamzy, was shot dead outside his Condell Park home.

Maha Hamze’s property was again shot at in February, resulting in a stray bullet piercing the window of Auburn Hospital and coming within inches of a nurse.

Days later, NSW Police expanded the state’s anti-bikie squad, Strike Force Raptor , amid a gangland war between the Hamzy and Alameddine families.

The ABC does not suggest the Alameddine family was behind any of the shootings targeting the Hamzy family.

Investigators spent the night swarming Bridge Street for CCTV and will be speaking with witnesses throughout the day.

It’s unclear why Bilal Hamze was targeted, but sources believe it may be drug-related.

-ABC