Police are bracing for revenge attacks after two women were gunned down in an unprecedented gangland attack on a south-west Sydney street.

It came as the family of one of the women paid a heartbreaking tribute to her and police made a public plea for information about the shootings.

The women, identified in reports as 48-year-old mother of two Lametta Fadlallah and Amy Hazouri, 39, were killed on Saturday night when the car they were sitting in was peppered with bullets.

A 16-year-old girl and a man, 20, were also in the car and police say they were “very lucky they were not killed as well”.

Ms Hazouri’s sister, Manal Raunegger, paid tribute to her in a social media post late on Sunday.

“Amy, you left us too soon my darling!” she wrote from Egypt.

“May Allah have mercy on you, the heart of your sister. I can’t believe it, you’re done, you won’t tell me again!”

Ms Raunegger also revealed a GoFundMe had been set up to raise money to take Ms Hazouri’s body to Lebanon for burial.

Police believe Ms Fadlallah, who had past connections to underworld figures, was the target of the attack. Her friend Ms Hazouri, a hairdresser, was caught in the crossfire as a volley of shots were discharged into the back seat of the car.

Homicide Squad commander Danny Doherty described the attack on a Panania street that left the women dead as “unprecedented” and “horrendous”. He said it had breached an unwritten gangland rule that protected women and children from attacks.

“It’s been long held, in the past that you don’t target children and women and family,” he told Sydney radio 2GB on Monday.

“If there’s a conflict between two criminal networks they will target each other.

“In this case we’ve just seen the rule book completely ignored and thrown out the window,” he said.

Criminal executions in Sydney over the past two years have led to more than a dozen fatal hits as gangs feud over turf and drugs.

“This one’s now a new low,” Detective Superintendent Doherty said.

Police are targeting criminal networks in south-west Sydney amid fears of revenge attacks.

“There’s always a fear of … some type of retribution,” Detective Superintendent Doherty said.he said.

Burned-out cars were found in nearby suburbs in the hours after the attack and police are investigating if they are linked to the shooting.

“These are the hallmarks of a planned attack; it was methodical, it was planned,” Detective Superintendent Doherty said.

Strike Force Laurantus has been established to investigate.

-with AAP