Police investigating the armed robbery of a fast food outlet in the Illawarra are appealing for a drive-thru customer who witnessed the incident to come forward.

About 10pm yesterday (Saturday 10 August), staff members were closing the fast food outlet on King Street in Warrawong when they were confronted by two men.

The pair had their faces covered and were armed with a metal bar and wooden plank.

They threatened staff before striking one on the head with the piece of wood.

The armed men stole cash before fleeing the scene.

Police from Lake Illawarra Local Area Command established a crime scene and they searched the area for the offenders without success.

The injured male staffer was treated at the scene for a minor injury.

Detectives will carry out a further canvass of the area today and will also attempt to view CCTV taken from the area.

They are particularly keen to speak with a woman who was sitting in her vehicle at the drive-thru window when the robbery began.

The woman in a yellow jumper drove away and police think she could have information which could help the investigation.