Only days after he was discharged from hospital after his car was sprayed with more than a dozen bullets at Bexley in Sydney's south on July 16 his mates were shocked to bump into him at the hairdresser.

The style-conscious 18-year-old was getting a trim.

"I don't think he [was the type] to hide," a long time friend of Hijazi said.

On Monday at 9.45pm Hijazi was shot at again, this time in a public car park less than a kilometre from where was ambushed a week before.

This time the outcome was fatal - Hijazi, who had links to the Comanchero bikie gang, was pronounced dead upon arrival at St George Hospital.

It was one of two fatal shootings in Sydney in the space of 15 minutes on Monday night. The other incident occurred at Earlwood, where debt collector Vasko Boskovski, 35, was killed.

Homicide Commander, Detective Superintendent Mick Willing, said police were on high alert after a "violent night for Sydney".

He said the fatal shootings at Bexley and Earlwood were in no way linked.

Both victims were known to police.

Friends of Hijazi said that the teenager did not appear to alter his life after he was first targeted and continued to live with his parents and two sisters in Sydney's south.

"He was so caring about others, he loved his mates, that's why he's so respected. Everyone is just shocked," a friend said. "When he got shot the first time most people thought of it as a warning. But they did it again which meant they wanted him out of the way."

Fairfax Media reported on Saturday that detectives were investigating if the first attack on Hijazi was linked to an internal feud within the Comanchero bikie gang.

Hijazi had links to the gang and is believed to have been tied to its controversial South Chapter.

Last month members from three other Comanchero chapters - the East, Wild West and Milperra, raided the Turrella clubhouse of the South Chapter.

Wearing all black and armed with guns and torches, the bikies stormed the clubhouse and told the 20 South members meeting inside that their chapter was to be closed down.

The South members were then told they could defect to one of the other chapters or "hand back your colours".

Friends of Mr Hijazi are paying tribute to him on social media.

Ali Mawassi wrote on Facebook that Mr Hijazi was one of two people in the same family to have died in recent days.

"Two losses for the family in two days.. This pain is unbearable. Every time I close my eyes in an attempt to fall asleep I see my loved ones faces," he wrote.

Ali Najem wrote: "RIP. Bassil Hijazi - Going to miss ya to death brother love ya !"

Monday night's violence comes after a wave of shootings across the city in the past month, in which two other men were shot dead.

Hells Angels nominee Tyrone Lee Slemnik was shot dead outside an apartment block on George Street in Eastlakes. Ali Jammas, who also had motorcycle gang links, was shot dead outside a home in Abbotsbury.

Last week, Detective Superintendent Scott Cook, who is overseeing the strike force set up to investigate public shootings in Sydney, said a number of other recent, non-fatal shootings were drug related.

"The cause of these shootings appears to be at this stage low-level drug dealing between hoodlums who now have firearms and consider themselves to be gangsters," he said at the time.

"They're two-bit pretenders. They're not gangsters. They're just young hoodlums with firearms. It's very reckless what they're doing. It's out of control in terms of their behaviour."

with Megan Levy