A 17-year-old school boy has been stabbed to death near a school in Sydney's north-west.

9news.com.au understands the boy was attacked by two others just after 5pm outside Ironbark Ridge Public School at Rouse Hill.

It is believed he was stabbed in the leg, and despite paramedics and a rescue helicopter rushing to the scene, the boy could not be saved.

It's understood the victim and the attackers were not students at the school, and two teenage boys were seen running from the scene after the incident.

The attackers, one of which is believed to have been wearing a school uniform, have not been found.

Police have shut down the area and are doorknocking on nearby houses to see if anyone witnessed the incident.

Member for Greenway Michelle Rowland said she was "deeply saddened" by the killing, and expressed her condolences for the boy's family.

"Deeply saddened to learn of the tragic loss of a young life in Rouse Hill this afternoon," she said in a statement on social media.

"My thoughts and deepest condolences are with the young boy's family during this extremely difficult time.

"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."

More to come.

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