The man, aged in his 40s, was shot in the doorway of a home in western Sydney about 3.15pm on Wednesday.
The victim, who is yet to be formally identified, died at the scene in Merrylands West despite attempts by paramedics to save him.
He had arrived as a visitor to the Bruce Street home just minutes earlier with a male resident and two young children, who were likely returning home from school, Detective Superintendent Simon Glasser told reporters.
The children were inside the home when the shots rang out, he said.
"There are a number of schools in the vicinity, a number of parks. This is a highly dangerous and reckless act that's been carried out here on a public street," Det Supt Glasser said.
The home owners were "very well known" to police for links to organised crime but the victim, who Det Supt Glasser said was likely a business associate, had no known criminal history.
"It's very early on in the investigation, however tragically that is a possibility that the wrong person has been shot by these offenders," he said.
Police have launched an investigation and are searching for a grey Audi sedan captured on CCTV leaving the scene westbound on Bruce Street.
It comes after multiple attackers were believed to have forced their way into a two-storey home in Glen Alpine, near Campbelltown in southwest Sydney, about 3.40am on Tuesday.
They then shot 23-year-old Marco Tapia dead in his bed as his family slept.
NSW Opposition Leader Kellie Sloane said the incident showed gangland violence was once again out of control.
''We need to be very clear about the threat on our streets and that is dangerous organised criminals ... innocent people have been in the firing line way too often,'' she said.
''Whether it is a young man, a student sleeping in his bed at night (or) a grandfather who's kidnapped and murdered."
She suggested the government was not doing enough to stop the shootings.
But Police Minister Yasmin Catley criticised the east Sydney-based MP's position on the state's gun buy-back scheme, launched after December's Bondi massacre.
''The member for Vaucluse, we must remember, is also the same person that wants to squash (national gun buy-back reforms),'' Ms Catley said.
''She wants more guns on the street and wants to blame the police for not doing their job ... I'm not tolerating that, I won't have a bar of that.''
NSW Greens leader Sue Higginson told AAP the tragic death was an awful reminder of the danger of guns in the community.
''This instant and irreversible act of gun violence that killed Marco Tapia this morning was only possible because guns are still accessible in the community,'' she told AAP.
Glen Alpine has one firearm for every 16.7 residents, she noted.
Mr Tapia's killers were at-large more than 24 hours after the savage home invasion.
The young man was not known to police and had nothing more than a traffic offence on his record.
Detectives are considering his death could be the result of a mistaken identity hit.
Mr Tapia's martial arts gym remembered him in a public tribute overnight.
''We lost a real one today,'' they wrote, adding ''rest easy Marco, one of us forever''.
An exiled alleged underworld identity posted to social media early on Tuesday that the perpetrators had mistaken their target.
''Popped the wrong person. Didn't even get the right house,'' Iziah Utai, alleged co-founder of the Coconut Cartel, wrote.
He returned on Wednesday to add: ''RIP Marco. #innocentvictim''.
The Alameddine network, a notorious crime family, and the Coconut Cartel, an emerging crime-for-hire network, have allegedly become embroiled in a feud, spilling into shootings across Sydney in recent months.
Campbelltown Acting Superintendent Gretchen Atkins on Tuesday said she was aware of online posts and said everything was under consideration.
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