Police have warned schoolchildren of the dangers of fights, after a 16-year-old boy died following a brawl with another teenager in south-west Sydney yesterday.

Detective Chief Inspector Mark Brett of Macquarie Fields Local Area Command said the boys, aged 14 and 16, "traded punches" during the fight at the corner of Durham and Kent streets, Minto, about 5pm.

The older boy stumbled back and fell to the ground a few hundred metres from Sarah Redfern High School in Monaghan Street, which both boys attended, police said.

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A passerby gave the victim first aid before he was treated by paramedics and taken to Campbelltown Hospital, where he died shortly after, police said.