Firefighters are busy preparing for tough weather conditions in Macarthur over the next few days.
Temperatures are expected to soar into the early 40s on Thursday and over the weekend.
The Green Wattle Creek blaze has already burned almost 150,000 hectares of land in the Burragorang Valley region since November 26.
Locals in Oakdale, Warragamba, Silverdale, Werombi, The Oaks, Lakesland, Thirlmere, Buxton, Balmoral, Bargo, Hill Top and surrounding townships are being urged to monitor conditions carefully as warmer weather settles in.
Southern Highlands Rural Fire Service Inspector David Stimson said the hot weather had put volunteers on high alert.
"This week we have been doing strategic back burns from Warragamba all the way down to Colo Vale," he said.
"This is not a contained fire so we don't want residents to get complacent - please make sure you are still monitoring conditions and have your active bushfire plan in place.
"Above all - please know what action you are going to take if the fire gets closer."
Locals were first warned to make preparations to leave and put their bushfire plan into action when the fire jumped Lake Burragorang earlier this month.
The NSW RFS downgraded the bushfire from Watch and Act to Advice on Tuesday (December 17).
There are more than 300 firefighters working to contain the blaze.
Inspector Stimson said spot fires had been popping up at different sites along the length of the fire.
"We have strike teams strategically placed along the interface of the fire so we can get out to these fires as soon as they are reported," he said.
"We have also been doing the back burning.
"We understand that the amount of smoke around has been making people nervous and anxious - but this is something we just have to do at the moment."
Inspector Stimson said their back burning plan was proving to be successful so far.
"If you look at the line of the fire it seems be going exactly as planned," he said.