Police were called to reports of multiple stabbings near Crawford Public School at Doonside about 3.40pm on Friday, shortly after primary students had left school for the holidays.

Before police arrived, an 18-year-old man and his 19-year-old brother were driven to Blacktown police station with stab wounds.

The younger man, identified in media reports as Iyzaa Naden, died at the station, while his older brother was taken to hospital in a serious but stable condition.

Two 15-year-old boys and a 16-year-old boy were arrested after attending Blacktown police station on Tuesday night.

They are due to face a children's court on Wednesday after being charged with murder and grievous bodily harm with intent to murder.

Another 16-year-old boy, who was also charged with murder, faced court on Saturday.

A 17-year-old boy has also been charged with accessory after the fact to murder and accessory after the fact to grievous bodily harm with intent to murder.

Police believe a group got off a bus near the school and a melee took place at the bus stop before the two teens were stabbed.

Investigators were looking into the possibility the incident was linked to local gangs amid so-called "postcode wars" involving teens in parts of western Sydney.

Australian Associated Press