Officials say hundreds of homes may have been lost after New South Wales suffered one of its worst bushfire days in recent memory on Thursday.

More than 90 fires - many of them uncontained - burnt around the state, fanned by strong wind gusts and high temperatures.

Thousands of people were evacuated as emergency warnings were enacted for bushfires burning out of control near in the Blue Mountains, and near Newcastle.

A number of fierce blazes in the Southern Highlands, Hunter and Central West also kept firefighters busy.

Rural Fire Service Commissioner Shane Fitzsimmons said he would consider it lucky if less than 100 homes were destroyed.

A cooler front passed through the state throughout the evening, but not before temperatures had hit the mid-30s and wind gusts reached 90kph earlier Thursday.