One person has been killed and six others have been injured following a three-car crash in Sydney's south this morning.

At about 6.10am on the Princes Highway in Waterfall, the three cars collided in the southbound lanes, knocking a Mitsubishi Outlander through the guardrail, down an embankment and towards railway tracks.

The car then rolled onto its roof. 

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The driver of the Mitsubishi died in the crash.

He has not yet been formally identified but is believed to be aged in his 60s. 

Six other people in two other cars were taken to hospital with varying injuries.

Police are appealing for any witnesses or anybody with dashcam footage to contact Sutherland Police Station.

One of two southbound lanes was closed on the Princes Highway approaching McKell Avenue, but all lanes have now been reopened.

Check the Live Traffic website for updates.

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