A 15-year-old accused of killing a fellow teen allegedly confessed to the attack by telling a police officer: “I stabbed another boy in the leg”.

The victim, a boy aged 17, died from stab wounds to his thigh after a confrontation at a park in Sydney’s north-west about 4.20pm on Monday.

About three hours later, the younger boy arrived at a police station with a parent and was subsequently charged with murder.

The 15-year-old, who cannot be identified for legal reasons, faced a children’s court on Tuesday.

Magistrate James Viney read a police application for DNA samples in the courtroom, which contained sworn declarations from an officer.

“It is asserted in the affidavit the victim was a 17-year-old with no criminal charges,” he said.

“It is asserted the young person set upon the deceased unprovoked and stabbed him in the groin area.”

The court also heard the 15-year-old was on police body-worn camera footage telling an officer “I stabbed another boy in the leg”.

When asked who he was admitting to stabbing, he allegedly gave police the name of the deceased.

Police allege witnesses described seeing the victim’s attacker dressed in a balaclava, hoodie, shorts and running shoes, a description allegedly matching that of the 15-year-old.

They argued scrapings taken from under his fingernails would likely contain DNA evidence that matched the deceased.

A court order is needed to take DNA evidence from an accused juvenile because they are not considered capable of giving informed consent.

The 15-year-old sat quietly in the courtroom, wearing a black hoodie and sporting a mullet haircut with shaved sides.

The boy did not apply for bail and was remanded in custody for eight weeks, when the case returns to court.

The stabbing happened in daylight within sight of numerous people walking nearby.

Authorities remained at the scene on Tuesday as locals laid flowers in tribute to the slain teen.

Police said those involved in the confrontation were not from the nearby school and officers believe it was not a random attack.

Several female witnesses who were in the park at the time rushed over to help the victim.

Paramedics were called but the teen died soon after.

“It would have been a horrifically confronting situation for those people and I can only praise them for their efforts,” Detective Superintendent Naomi Moore told reporters on Monday evening.

“It was a potentially dangerous situation they were walking into, but they thought nothing of themselves to go in and render aid.”

NSW Premier Chris Minns sent his condolences to the teenage boy’s family and friends.

“I am deeply saddened by the death of a teenage boy at Rouse Hill and extend my sincere condolences to his family and friends,” he said in a statement.

“It is an unimaginable loss, and the whole community will feel the impact.”

Local federal MP Michelle Rowland said she was deeply saddened by the incident.

“There is no place in our community for these acts of senseless violence, and I know this news will be particularly distressing for local families,” she said.

The accused murderer is scheduled to return to court on January 23.

–AAP