Police are appealing for public assistance following the armed robbery of a fast food restaurant in south-western Sydney yesterday.

About 8.45pm, a man approached the restaurant on Stockland Avenue, Moorebank, armed with a knife and with his face concealed.

The man threatened the 29-year-old store owner as he was closing the restaurant, demanding money, before he ran from the scene with a significant sum of cash.

Police were notified and officers attached to Liverpool Local Area Command attended, established a crime scene and canvassed the area.

The man is described as being approximately 175cm tall and of muscular build. At the time he was wearing a grey hooded jacket with a red logo on the front, and dark-coloured pants.

It is believed the man ran from the scene with two other men who were waiting outside.

Police are appealing for anyone who witnessed the robbery or any suspicious activity in the vicinity of Stockland Avenue, to come forward.

Anyone with information should contact Liverpool Police via Crime Stoppers on 1800 333 000.