An police chase has ended in a crash between a car and truck in Western Sydney.

Two teens are accused of stealing a car from Blacktown Hospital before leading police 30 minutes west on Thursday afternoon.

Police tried to stop the car on Francis Rd at Rooty Hill, but the teens allegedly did not stop, and continued to the intersection of Forrester Rd and Hatherton Rd at Tregear, where they crashed with a semi-trailer about 12.30pm.

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The alleged driver, a 17-year-old girl, suffered minor injuries and was treated by NSW Ambulance paramedics.

The alleged passenger, a 16-year-old boy, was seriously injured.

Both teens were taken under police guard to Westmead Hospital in stable conditions.

The truck driver was not injured, and will undergo mandatory testing.

Investigations into the crash are ongoing.

The teen driver and her passenger were hospitalised, while the truck driver was not injured. Credit: 7NEWS