Police discovered a petrol container near the unit on Guildford Road at Guildford just before 11.30pm on Thursday, and detectives believe the fire was deliberately lit.

No-one was inside the ground-floor unit when it went up in flames, however one woman from the apartment block was taken to Westmead Hospital where she was treated for smoke inhalation.

A short time after the blaze was extinguished, police discovered a 39-year-old man sitting in a car in Eastern Avenue in Revesby with serious burns to his upper body.

Police would like to question him over the fire, however he was too seriously injured and was taken to the Royal North Shore Hospital. He was in an induced coma on Friday morning.

A crime scene has been established at the unit block and forensic police are examining the unit.

Anyone with information about the fire has been urged to call Crime Stoppers on 1800 333 000.