More than 1000 firefighters worked into the night and on Thursday morning there were 75 fires still burning across the state, at least 10 of which were out of control.
Temperatures were expected to peak in the low-mid 20s in Sydney and surrounds, while the weather was forecast to be cooler with showers on the south coast.
But hot conditions were expected to continue in the state's north, including peaks in the mid-30s as a number of grass and bush fires burned in the region.
A strong wind warning was also in place for much of the NSW coast.
The forecasts come after the state sweltered for days with maximum temperatures 10C to 15C above the September average.
A total fire ban remains in place for the NSW northwestern region, which includes the Moree Plains, Narrabri, Walgett and Warrumbungle council areas.
Fire danger ratings are also high in the far north coast, New England, Greater Hunter, northern slopes and upper central west plains regions.
Premier Chris Minns was worried about the longer-term risks posed by the soaring temperatures given that it was still early spring.
"It's September and we're already experiencing four days in a row of temperatures above 30 degrees with high winds," he said on Wednesday.
"We are concerned about a horror summer."
19°C