Several homes were destroyed in Thursday's fires, the New South Wales Rural Fire Service says. There were no reports of injuries or deaths.
The number of destroyed homes was unknown, with conditions too intense for firefighters to reach the hardest-hit areas. Authorities said they would not know how many homes were destroyed before dawn on Friday. Eighteen fires were out of control.
Smoke from the fires blocked the sun over central Sydney, casting an eerie haze over the city.
Wildfires are common throughout Australia in the warmer months. In February 2009, wildfires killed 173 people and destroyed more than 2,000 homes in Victoria state.