Five people were forced to flee a burning townhouse in Bomaderry on Monday night.
Two men suffered burns to their hands and were treated by paramedics after the blaze, which occurred on Karowa Street and began about 9.50pm.
Inspector Norman Buckley from Fire and Rescue NSW said it took just minutes for the fire to take hold.
When fire crews arrived the two-storey home, which was split into two units, was well alight, with fire already engulfing the roof section of the top storey.
It took firefighters just nine minutes to arrive on scene. However, the blaze was still able to destroy about 70 per cent of the building.
Insp Buckley praised the efforts of fellow firefighters, who managed to stop the fire spreading to nearby townhouses.
"Along with the attack on the main fire they protected the exposures and none of those exposures were in danger except for minor smoke penetration," he said.
Shoalhaven police inspector Bruce Griffin said the blaze was believed to be due to a faulty power point.