Police have appealed to anyone with information about the fatal stabbing of a 22-year-old man in Beaumont Street Hamilton early on Sunday morning to come forward.
Paramedics were called to the popular nightlife strip at 2.40am following reports that a man in his 20s had been stabbed near the post office.
A police officer and members of the public were already attempting to treat the man's "significant stab wounds".
The man was rushed to hospital but could not be saved.
He is yet to be formally identified.
Detectives spent Sunday interviewing witnesses and collecting evidence, including CCTV footage, from the area.
Police revealed that the man had been stabbed during a violent altercation with a group of people.
"It's important for us to understand what happened to this young man," Superintendent Kylie Endemi said.
"It's important for us to do that so we can assist his poor family in understanding how and why this young man passed away.
"They are going through every family's worst nightmare."
Strikeforce Mannum has been launched to investigate the incident.
Police believe the man was accompanied by a couple of friends prior to becoming involved in the altercation.
Superintendent Endemi appealed to anyone with information which could shed light on the tragedy to come forward.
"We are making a plea to anyone who might have information. Whether you were there and witnessed something or whether you know something subsequent to that incident occurring. We know that there are people out there that have information that will assist us," Superintendent Kylie Endemi said.
"We ask them to think about the fact that a young, 22 year-old person has lost his life today and there is a family who is in deep mourning, trying to come to terms with the circumstances of that."
"So we make that plea, please come forward, help our investigators find out who is responsible for this terrible incident."
Hamilton resident Leigh Dryden said he heard "the usual noise, the yahoos coming home from the pub at about 2.30am".
"There was screaming and carrying on, then an absolute plethora of sirens," Mr Dryden said.
"Because you hear it so much, you don't tend to think about it. Then I saw the road blocked off this morning and thought 'gee whiz something's happened'."
Mr Dryden lives one street down from the Kent Hotel, where police were seen investigating the incident on Sunday morning.
"From what we understand, a young guy was stabbed outside the post office," he said.
"There's reports the guy dropped his thongs and left in a getaway car and they had his DNA.
"People were jumping on the speculation bandwagon."
Mr Dryden said it was "sad that we have to endure incidents like this on our doorstep, and more importantly a young life has been taken".
He had a work colleague staying with him last night.
"We got up and there was a lot of noise," he said.
"But we're used to drinkers coming home from the Kent at 3am. You don't tend to pay a lot of attention to it. It comes and goes.
"But there was definitely a real kerfuffle. I don't know if they've come out of the Kent or what's happened.
"The Kent is the closest to the post office. The Northern is a little bit further down."
Businesses were feeling the effects of the police road closure on Sunday morning.
"There was a murder in the early hours, so the street's been closed off from the Piggott's chemist," Brenda, of Qs Books said.
"Some of the back streets are closed as well.
"It has affected everybody and all the businesses because they can't come up the normal route.
"All I heard was somebody was stabbed out the front of the post office."
NSW Ambulance paramedics treated the victim before taking him to hospital.
He later died there but had not been formally identified, NSW Police said.
A witness at the hospital said "I just remember all the busyness of the doctors and nurses".
"They all disappeared into a room. One person said I would hear on the news that the guy had died."
Police established a crime scene in Beaumont Street, where they were investigating on Sunday.
The State Crime Command's Homicide Squad was involved.
"Beaumont Street is closed between Tudor and Donald streets, with motorists and pedestrians advised to avoid the area," the police statement said.
A report will be prepared for the coroner.
Anyone with information, dash-cam or mobile phone footage filmed there can call Crime Stoppers on 1800 333 000.
