A teenage boy has been stabbed to death in a brawl in Sydney's west and another is seriously injured, police say.
Officers rushed to the corner of Suffolk and William streets, Blacktown, about 10pm on Thursday to respond to the fight and found four people with stab wounds.
One teen died at the scene despite the best efforts of paramedics and another was taken to hospital in a serious condition.
Police said two more males, whose age wasn't released, suffered non-life-threatening injuries.
An investigation is underway and police say several people are assisting with their inquiries.