Cooler weather continues to bring relief for fire fighters working to extinguish a large blaze at Winmalee in the lower Blue Mountains.

More than 200 firefighters worked throughout the night to try and contain the fire that has burned over 1,000 hectares since Tuesday.

Joel Kershaw from the Rural Fire Service says winds are not as strong and temperatures have dropped, giving crews an opportunity to strengthen containment lines.

"There was quite a bit of back burning done, in and around the yellow rock area," he said.

The New South Wales Rural Fire Service has issued advice for the bushfire on its website, along with another major fire that started at Londonderry in Sydney's west earlier in the week.

An investigation has been launched into hat sparked the bushfires.

Some residents in Winmalee returned home yesterday to survey the damage.

At least two houses are expected to remain without power until later today.

There are 70 fires still burning across New South Wales, 20 of those are classified as uncontained.

Meanwhile, weather forecasters say heatwave conditions will continue across parts of Queensland today after the mercury has soared across the state.

Yesterday, in the south-east, temperatures were in the early 30s - Brisbane reached 31.5 degrees Celsius. In the far northwest, it was up around 39C.

Bureau of Meteorology senior forecaster Matthew Bass says that region could top 40C today, the earliest 40-degree day on records for Queensland.

The heat looks like hanging around through at least until about next Monday or Tuesday.