A 33-year-old man is in a critical condition in Westmead Hospital following a single-vehicle accident in Blayney, west of Bathurst.

The man was a passenger in a vehicle being driven by a 45-year-old man when it veered off Millthorpe Road just before 7pm on Thursday.

He was treated at the scene before being airlifted to Sydney and it is believed he will be transferred to Royal North Shore Hospital.

The driver suffered minor injuries and was taken to Orange Base Hospital.