Police are treating a fire in a townhouse at Casula in Sydney’s south west last night which prompted the evacuation of 50 people as suspicious.

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Emergency services were called to the townhouse on Myall Road just before 1:00am where they found the house well alight.

Police said they did not believe anyone was home at the time however more than fifty people had to be evacuated from nearby units. Two of the units suffered smoke damage.

Two elderly people were treated for smoke inhalation while a 30-year-old man was taken to hospital in a serious condition after cutting his arm while helping to evacuate residents.

Nearby residents had reported smoke coming from inside the townhouse.

Police have established a crime scene which is being examined by forensic teams to determine the cause of the blaze.