Police said the teenager was riding along the Eleven Mile Drive when he swerved in front of an Isuzu truck travelling in an easterly direction two kilometres from the Gilmour Street intersection.

Chifley Police District duty officer Inspector David Abercrombie said the truck driver had told police he was coming over the crest of a hill on Eleven Mile Drive when the incident occurred.

The driver told police that the teenager, who was riding a scooter, suddenly and without any warning swerved in front of the truck, hitting the vehicle.

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The impact knocked the teenager to the ground. He was not wearing a helmet, and the law does not require scooter riders to wear a helmet.

Inspector Abercrombie said the teenager, who suffered a laceration to his head in the accident, was incredibly lucky not to have been more seriously injured.

A spokesperson for NSW Ambulance said they received a call to the incident at 3.15pm.

Three ambulances were sent to the scene where paramedics treated the injured scooter rider.

"We responded to reports a child riding a scooter had been knocked [over] by a truck," the spokespeson said.

"We arrived at the scene and treated an 18-year-old male who had no obvious injuries apart from a graze to his head and large abrasion to his hip.

"He was transported to Orange Base Hospital via road ambulance in a stable condition."

Approximate location of the crash ...

Police said while there was no specific offence for not wearing a helmet while riding a scooter, it was still likely that the teen would be issued tickets for his role in the crash.

Officers investigating the circumstances of the crash expect to write tickets for the teenager for failing to keep to the left of the road and riding a scooter on a road with a speed limit greater than 50km/h.