A man used a syringe and a knife to carjack a young woman in Sydney before he crashed her vehicle through a boom gate during his escape.

The 26-year-old victim was sitting in her Mazda 3 in a carpark at a Haymarket shopping complex, in inner Sydney, when the offender approached her about 6pm (AEDT) on Tuesday.

Police say he forced her out of the vehicle and drove through a lowered boom gate as he left the car park.

The woman was uninjured in the incident.

AAP vpm/