The mercury is expected to reach 41 degrees Celsius in Sydney and Penrith and while it will be slightly cooler in the east, Bondi is still forecast to reach 39C.

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

To the state's west, dust storms were also moving east after it darkened the skies above the southern states and turned the horizon orange

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

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

The NSW Rural Fire Service (RFS) has issued "severe" fire dangers and a total fire ban across seven regions.

They are the Greater Sydney, Greater Hunter, Illawarra/Shoalhaven, Southern and Central Ranges, North Western and Far South Coast.

RFS spokesman Greg Allen said recent rain had been helpful, but more than 60 fires were still burning across the state.

"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."

BOM forecast 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."

Mr Shabren also said the state's South Coast and south-east could also be hit by "very, very strong and damaging winds" which began last night and could persist this morning.

Those gusts were sweeping the east of Riverina, the Snowy Mountains, the NSW South Coast and parts of the southwest slopes.

The BOM said the dust storms which blanketed Broken Hill, in the state's far-west on Wednesday, would be stopped by the mountains in the Central Ranges.