Police from the Mt Druitt Local Area Command are investigating the circumstances surrounding an armed robbery at a fast food store overnight.

About 8.45pm (Monday 21 May 2012), the store manager was the sole employee behind the counter of the pizza restaurant on Rooty Hill Road when three men entered the store.

Two of the men, who had their faces covered, jumped the counter and threatened the manager with a knife.

They pushed him to the floor, demanding that he open the till.

The employee handed over a sum of cash before the men fled the store, last seen heading north on Rooty Hill Road.

A crime scene was established and officers from the Forensic Armed Robbery Unit attended.