A police officer has been left with serious injuries and his partner was left trapped after a car crash in Sydney's west overnight.

At about 7.15pm, emergency services were called to the intersection of Church Street and Parramatta Road in Parramatta.

They found a marked police car which had crashed into a guardrail.

The vehicle had been on its way to a priority incident, with its beacons on, when the crash took place.

The driver, a 24-year-old constable, was uninjured.

He was subjected to a roadside breath test which returned a negative result.

The passenger, a 23-year-old probationary constable, was trapped in the car and had to be freed by firefighters.

He was treated at the scene for an arm injury before he was taken to hospital in a serious condition.

A critical incide

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