Firefighters continue to battle some of the most destructive bushfires to ever strike Australia's most populous state, with higher temperatures and winds expected to intensify the danger in the coming days.
While dozens of blazes in New South Wales have been contained, 58 were still alight on Monday and 14 of them out of control, enveloping Sydney in a thick white smoke haze that prompted warnings for people to stay indoors and avoid exercising.
The main area of concern was near the town of Lithgow west of Sydney where a huge fire that has already burned nearly 40,000 hectares was threatening the communities of Bilpin, Bell, Clarence and Dargan.
Officials fear intensifying heat and winds on Tuesday and Wednesday could push it into another blaze at nearby Mount Victoria in the Blue Mountains and then move towards the populated areas of Katoomba and Leura.
"I don't think I've ever used the word mega-fire," said New South Wales Rural Fire Service Commissioner Shane Fitzsimmons.
"But the reality is that the modelling indicates that there's every likelihood that in the forecast weather conditions that these two fires, particularly up in the back end of the mountains, will merge at some point."
Firefighters spent the night building containment lines to try and prevent this happening ahead of a predicted deterioration of weather conditions.
The fire chief played down earlier suggestions that all communities in the Blue Mountains, where 76,000 people live, could be evacuated.
"We are not planning a mass evacuation of the Blue Mountains community," Fitzsimmons said.
The premier of New South Wales state, Barry O'Farrell, has declared a state of emergency in an effort to force evacuations if needed.
The fires have killed one man, destroyed a total of 208 homes in New South Wales state and damaged another 122 since Thursday, the Rural Fire Service said.
Officials said temperatures in the fire zone on Sunday exceeded 25C, winds reached 20km/h and humidity dropped to 30 per cent.
The Defence Department, meanwhile, said it was investigating whether there was any link between the Lithgow fire, which started on Wednesday, and military exercises using explosives at a nearby training range on the same day.
Arson investigators are examining the origins of several of more than 100 fires that have threatened towns surrounding Sydney.
The bushfires have been extraordinarily intense and early in an annual fire season that peaks during the southern hemisphere summer, which begins in December.
In February 2009, wildfires killed 173 people and destroyed more than 2,000 homes in Victoria state.