Although fire grounds across the state have received rainfall in the past week, the NSW Rural Fire Service has warned forecast high temperatures and winds could see fire activity increase on Thursday.

Temperatures are expected to reach 40C in Nowra on the South Coast, 43C in Penrith in western Sydney, 41C in Cessnock in the Hunter region and 42C in Bulahdelah on the mid-north coast.

NSW RFS spokesman Ben Shepherd said low humidity and very strong northwesterly winds have crews bracing for a potentially dangerous day.

"There is a broad area of severe and very high fire danger and areas of extreme fire danger," Mr Shepherd told AAP on Wednesday.

"All fire grounds have received some rainfall and that has greatly reduced some fire activity but we might still see some fire grounds pick up and move tomorrow."

The ACT Emergency Services Agency on Wednesday issued an emergency warning for an out-of-control bushfire burning on the eastern fringe of Canberra.

The agency urged people in the suburbs of Beard and Oaks Estate to leave immediately towards Queanbeyan across the NSW border.

Total fire bans are in place in NSW for Thursday in the greater Sydney, greater Hunter, Illawarra/Shoalhaven, southern ranges, central ranges and north western fire districts.

Severe fire danger ratings are also in place for these regions.

The Bureau of Meteorology on Wednesday issued a severe weather warning for damaging winds for parts of NSW's south and west.

Strong to gale force winds were forecast to continue into Thursday.

The BOM warned Wednesday evening's and Thursday's damaging winds may extend to the southern tablelands and parts of the central tablelands, the Illawarra and south coast.

The warning comes after severe thunderstorms hit Sydney, Newcastle and Wollongong on Monday, leaving homes and businesses without power.

Almost 70 fires continued to burn across the state on Wednesday night.

Australian Associated Press