A 13-year-old boy is one of two teens charged with murder after they handed themselves into police following a fatal stabbing at a shopping centre.

A man in his 30s died on Cleeve Close in Mt Druitt, western Sydney, on Friday night.

Police found the man on the street, suffering stab wounds to his torso, behind Westfield Mt Druitt about 9pm.

He died before paramedics could arrive, despite the officers' best efforts to save him.

Authorities issued a public appeal for assistance on Saturday and conducted a two-day investigation.

On Sunday evening, a 13-year-old attended Mt Druitt police station, where he was arrested.

He was charged with murder, breach of bail and received an unrelated charge of robbery in company.

About 40 minutes later officers arrested a 16-year-old boy at a home in Cabramatta.

He was charged with murder, accessory after the fact to an offence.

Both boys were refused bail to appear before a children's court on Monday.

Blacktown commander Superintendent Brendan Gorman on Saturday told reporters detectives were open to several possibilities and looking for "about a dozen people in the area at the time" to assist their investigation.

A number of items were seized at the scene on Friday, with the attack described as having been carried out with a bladed weapon.

The circumstances of the initial interaction were then unknown and it was still to be determined whether the slaying was random or targeted.

"At this stage, I would say it's a horrendous incident and it's certainly concerning for police," he said.

The deceased - who at the time was not formally identified - was believed to have "some history" with police, and possible gangland links were one of detectives' many lines of inquiry.

Video footage from numerous sources will help officers patch together the train of events.

"Police have seized a number of videos from CCTV and also mobile phone videos that have been circulated," Supt Gorman said.

CCTV vision, published by media outlets and allegedly depicting the incident, showed a group of several men walking along a street before a man threw a punch and was attacked by three others in retaliation.