Man threatened with gun in Sydney

A man has been assaulted and threatened with a gun by three men who then stole his car and wallet in Sydney's southwest.

Police said the 22-year-old was cleaning at a business at Blair Athol near Campbelltown at 12.30am (AEDT) on Sunday when the incident happened.

The trio fled the scene in the man's car with cash, as well as his wallet.

The injured man was taken to Campbelltown Hospital and treated for non-life-threatening abdominal injuries.

Police are appealing for witnesses or anyone with information about the incident to contact them.

The men are only described as wearing dark clothing and hooded jackets.