Emergency services were called to the unit in Punchbowl about 10pm, after neighbours sounded the alarm.
On arrival, officers found the unit well alight.
NSW Ambulance paramedics treated an unconscious man who was found inside the property, but he died at the scene.
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Police have established a crime scene and are investigating the cause of the fire.
Anyone with CCTV footage or information about the incident are urged to contact Bankstown police or Crime Stoppers on 1800 333 000.
