A woman has died in NSW after the car she was driving crashed into a tree.

The woman was alone in the car when it struck a tree in Appin, about an hour-and-a-half southeast of Sydney, at about 1.15pm.

Emergency services responded at the scene between Armstrong Rd and Copperfield Dr, which is about 2km of the Appin Bypass, where footage shows the front of a white vehicle completely destroyed.

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The driver died at the scene, NSW Police said.

She is yet to be formally identified.

Appin Rd is expected to be closed until about 5.30pm, and traffic diversions are in place, police said.

Anyone with information or dashcam footage is urged to contact Crime Stoppers.