WA Police have issued an urgent alert after responding to the hold-up of a firearm store in Busselton.

Police say they attended the scene at 8.50am after a man allegedly robbed the store with a pistol, stealing a rifle and ammunition.

He was last seen leaving in a silver vehicle, believed to be a Holden Commodore. He has been described as light-skinned, between 25 and 30 years old, of medium or stocky build with dark hair under a cap.

Anyone who has seen him has been urged to contact police on 131 444.