Fire crews ramped up containment efforts around several of the blazes with the weather forecast to deteriorate and officials warning of "unparallelled" dangers.
More than 200 homes have already been destroyed and another 120 damaged by the wildfires, which broke out across New South Wales state in unseasonably warm weather earlier this week, fanned by extremely high winds.
The worst of the fires, in the Blue Mountains west of Sydney, plunged the city last week into an eerie midday darkness as plumes of smoke and ash filled the sky.
Firefighters had a reprieve on Friday and yesterday with an easing in the weather, but containment and property protection efforts were stepped up today ahead of an expected intensification in weather conditions set to include warmer temperatures and 100 kilometre per hour (60 mile per hour) winds.
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New South Wales Rural Fire Service Commissioner Shane Fitzsimmons said there would be several extremely difficult days ahead for fire crews.
"We've got what would be unparallelled in terms of risk and exposure for the Blue Mountains and Hawkesbury communities throughout this week," Fitzsimmons told reporters.
"The reality is, however, these conditions that we're looking at are a whole new ball-game and in a league of their own."
State premier Barry O'Farrell said crews had carried out controlled burn operations through the night to strengthen buffer zones around the major Blue Mountains fires and "are on alert to switch to active firefighting if properties come under threat".
A total fire ban was in place in the Greater Sydney and three other regions across the state until further notice.