Hot winds and low humidity are forecast to fuel fresh bushfires around much of largest city after firefighters worked through the night to contain main troublespots.
"It's not looking favourable for our firefighters," Ms Nicole Ingram of the Rural Fire Service said.
Cooler temperatures and low winds yesterday, which provided a single day of comparative respite from the bushfires, were expected to give way another phase of hot, dry weather.
Sydney was covered in a thick blanket of acrid, purplish smoke for its second successive morning today, ahead of forecast winds of 25 miles an hour.
Forecast humidity of less than 10 per cent and temperatures of 35 degrees Celsius signalled perfect bushfire conditions.
"Today, all the containment lines will be tested. If they hold, that's great. But there's a chance that they may not," Mr Cameron Wade of the Rural Fire Service said.
One person has died in the bushfires since Wednesday as more than 4,000 local and interstate fighters, backed by 91 aircraft, most of which are water-bombing helicopters, have struggled to halt the blazes.
Officially, 33 houses have been destroyed by the fires since Wednesday. But an accurate assessment of the damage was hampered by the difficulty in picking out homes from other structures in the charred wreckage left in the wake of the bushfires adding many caravans, sheds and vehicles had been lost.