One person has been killed and two others, including a child, are injured following a serious car crash in Sydney's north-west.

The incident occurred shortly before 4pm on Castlereagh Road at Agnes Banks, involving a Holden Commodore and a Nissan ute that was towing a trailer.

The driver of the Holden, a man believed to be in his 40s, died at the scene.

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A 10-year-old boy who was the sole passenger of the Holden was taken to Westmead Hospital under police escort in a critical condition.

The driver of the Nissan, a man in his 20s, has also been taken to Westmead Hospital in a serious condition.

Police officers from the Nepean Area Command have established a crime scene and an investigation is underway into the circumstances leading to the crash.

Police are urging anyone who may have dashcam footage of the incident to contact police immediately.

A report will now be prepared for the information of the Coroner.

Anyone with information about this incident is urged to contact Crime Stoppers: 1800 333 000 or https://nsw.crimestoppers.com.au.