A 14-year-old boy is dead after a three-vehicle crash in northern NSW.

Police were called to the Kamilaroi Hwy at Wee Waa — about two hours north-west of Tamworth — about 3pm on Sunday where they found a semi-trailer, tractor and a horse truck towing a caravan had been involved in an accident.

An unidentified member of the public, who was not involved in the crash, provided first aid to the boy, who was a passenger in the horse truck. He was also treated by paramedics but died at the scene. Police believe the man may be able to assist with their investigations.

The driver of the horse truck, a 38-year-old man, was taken to hospital in a stable condition for mandatory testing and treatment while the 66-year-old tractor driver and the 33-year-old semi-trailer driver, both male, were uninjured but also taken to hospital for mandatory testing.

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One horse in the truck was euthanised due to injuries sustained in the crash with three others taken away for treatment.

Police are urging anyone with information or who can help identify the man to contact Crime Stoppers.