Police are investigating the armed robbery of a petrol station at Doonside last night.

About 7:15pm, Monday 10 November 2014, a man entered the petrol station on Hill End Road while carrying a back pack.

Police have been told the man walked to the counter and asked for a packet of cigarettes before producing a pistol from his bag.

He threatened the console operator and demanded money from the register. The man was handed cash and left the store.

Police from Blacktown Local Area Command were called to the petrol station where they established a crime scene which was examined by forensic officers.

Detectives are continuing investigations and are looking for a man described as being of Caucasian appearance with a tanned complexion, aged in his 20s, 180cm tall with a medium build and wearing a black baseball cap, black hooded jumper and carrying a black backpack.