A police officer has serious head injuries after being hit by a car in the southern NSW Snowy Mountains region.

The constable was pursuing a stolen ute on the Monaro Highway at Nimmitabel, about 10 kilometres outside of Cooma on Monday night.

Police say the ute then stopped, the driver got out of the car and started to run.

The pursuing police officers also stopped and the male constable gave chase.

The fleeing man then got into a white sedan which hit the policeman.

The constable has serious head injuries. He was treated at the scene before being flown to Canberra Hospital in a stable condition.

A crime scene has been established as investigations into the crash get underway by officers from Monaro Police District.

Police will address the media later on Tuesday.