Fire Inspector Glenn Launt praised neighbours who ran to help two men who were inside the home at the time.
The occupants were trapped and could not open the door.
The fire started just after 1:00pm and it took 40 firefighters more than two hours to bring the blaze under control.
One of the occupants was taken to Nepean Hospital with minor hand burns and the other was treated at the scene for suspected smoke inhalation.
An eyewitness, Teddy Webber, who lives five houses away, said at first it was thought more people were trapped inside the house because of the panic.
But he said police worked out that was not the case.
Mr Webber said the fire looked dangerous and he ran to alert other neighbours.
“I ran up the street, and went to the lady around the corner … she was concerned it was hers, but the flames were coming out of the two windows in the front and the garage, and they were nearly across the road, they were leaping in and out of the garage across the road,” he said.
Superintendant Ian Krimmer from NSW Fire and Rescue said they stopped the flames from spreading to neighbouring properties. He said they have yet to determine the cause of the blaze.