A teenage P-plate driver has been charged with dangerous driving after a pregnant woman and her unborn child were hit and killed in a two-car crash.

Ambulance paramedics treated the woman, who was eight months pregnant, at the scene before she was taken to Sydney's Westmead Hospital in a critical and unstable condition but she and her baby were unable to be saved.

The woman had been walking with her husband and three-year-old son when she was struck by a vehicle at the entrance to a car park at Hornsby in the city's northwest on Friday evening.

A 19-year-old man behind the wheel of a BMW and a 48-year-old male driver of a Kia station wagon were uninjured.

Both were taken to Hornsby Hospital for mandatory testing.

Traffic and Highway Patrol Command assistant commissioner David Driver d

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