Boy dragged for 2km through Sydney before falling from car, police say

A teenage boy was allegedly dragged by a car for two kilometres through Sydney streets, suffering serious injuries overnight.

Police said that shortly before 7pm, a 15-year-old boy and a 19-year-old man met for a "transaction" at Forge Street, Blacktown.

Sitting in the 19-year-old's car, they began arguing before the man drove away with the 15-year-old.

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Detective Chief Inspector Jason Pietruszka said that the 19-year-old drove "at speed" along Sunnyholt and Vardys roads.

He said a second car, driven by somebody known to the 15-year-old, had "interacted" with the first car, after which the boy fell onto the road.

Pietruszka said it is believed the 15-year-old had been hanging from the passenger side window, but the exact circumstances of his exit from the car were yet to be determined.

The boy was taken to Blacktown Hospital before being transferred to The Children's Hospital at Westmead, where he remains in a serious but stable condition.

Pietruszka said he had suffered multiple facial fractures and other injuries yet to be determined.

The boy was believed to be in an induced coma.

A car was stopped on Sentry Drive at Stanhope Gardens a short time later.

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The 19-year-old male driver was arrested and charged with dangerous driving occasioning grievous bodily harm, negligent driving occasioning grievous bodily harm, and supply a prohibited drug.

The Riverstone man was refused bail to appear at Parramatta Local Court today.

Police are appealing to anybody who may have seen a red Mazda 3 in the area around the relevant time, or who has dashcam vision, to call Crime Stoppers on 1800 333 000, or online.