Homes have been lost to out-of-control bushfires in NSW with temperatures hitting 40 degrees Celsius in parts of the state.

Key points: There are reports of property losses on the south coast

There are reports of property losses on the south coast The public were urged to curb electricity use due to damage at some power stations

The public were urged to curb electricity use due to damage at some power stations The BOM is forecasting a temperature drop for Friday

The NSW Rural Fire Service (RFS) said it would be a "long afternoon and night", confirming that homes had been lost in the far south coast towns of Moruya and Bermagui.

There was also a report of property loss in the Bundanoon area.

As of midnight, there were no bushfires burning at emergency level.

The NSW Minister for Energy & Environment Matt Kean had urged the public to curb electricity use between 4.00pm and 8.00pm due to fire damage at some power stations.

The Box Hill fire has been downgraded to watch and act. ( Supplied )

Canberra Airport closed for several hours on Thursday because of a nearby grass fire.

Earlier, a bushfire in the Hills District threatened the suburbs of Box Hill and Nelson, around 40km from the Sydney CBD, but has since been brought under control.

The temperature in Sydney hit 41.3C.

Penrith hit a high of 42.4C while Sydney Airport was the hottest part of the city at 43.3C

A southerly change is expected to reach Sydney about 11.00pm.

The NSW Department of Planning, Industry and Environment also issued a poor air quality forecast for Sydney.

Dust storms are moving across the far west and elsewhere a late southerly will bring damaging winds and the risk of dry lightning strikes.

A forecast of temperatures across the state for 1:00pm Thursday. ( ABC News )

While the Bureau of Meteorology (BOM) is forecasting a 12C drop in some areas for Friday, firefighters braced for another "challenging" day.

The latest high-risk conditions come as the Member for Bega, Andrew Constance, criticises the Red Cross for not distributing donations quickly enough.

RFS spokesman Greg Allen said recent rain had been helpful, but many fires are still burning.

"Certainly some rain has helped in strengthening containment lines over the last couple of days," he said.

"We have seen rainfall across fire grounds but in some cases, not the entirety of [the] ground and not enough rain to put the fire out completely."

People enjoy the hot weather at Sydney's Balmoral Beach. ( AAP Image: Bianca De Marchi )

BOM forecaster Abrar Shabren said there was a potential for lightning storms and strong winds to rekindle fires extinguished by last week's downpour.

"If dry thunderstorms do develop over forests or fire grounds that can be problematic for firefighters on the ground," he said.

"They can cause new ignitions and old fires can get flared up as well with those very gusty, strong winds."