Conditions had improved Monday as winds eased, with firefighters working to slow the spread of the flames.
A blaze at Menai still continues to burn in a south easterly direction toward Barden Ridge - no homes are at risk but crews are on the ground focused on containing the fire.
Mr Fitzsimmons said it was possible that winds could strengthen again and elevate the fire danger.
The RFS is now advising residents in Pleasure Point, Sandy Point, Alfords Point, Barden Ridge, Voyager Point, Illawong, Menai & Bangor to "remain vigilant throughout the day and keep themselves up to date by checking the NSW RFS website". Several residents report fighting off embers with hoses and water buckets.
Major roads separating bushland and residences were cut off in some areas, and fire services used helicopters to dump water over key points.
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The Holsworthy fire - which has burned 1000 hectares - resulted in hundreds of people leaving their homes on Saturday evening with flames nearly reaching properties at Holsworthy and Wattle Grove and spot fires later threatening Sutherland and Menai.
It's unclear if Friday's fires reignited on Saturday or if someone may have deliberately lit the blaze which has now burned through nearly 2500 hectares of bushland focused on the Holsworthy military range.
On Sunday, more than 500 firefighters in nearly 100 fire trucks, along with 15 aircraft, battled the blaze throughout the day.
"There is plenty of work ahead", the commissioner said.
The blaze was downgraded from watch-and-act to advice about 2am on Monday.
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He said the aircraft had unfortunately already been returned to the United States because they were always sent back by the end of March when temperatures were traditionally cooler.
"We have taken a number of statements from people who called the police and fire services in regards to the fire".
"We're certainly looking to maximise the amount of time we have them here".
New South Wales police have declared the area a crime scene but the RFS says it is too early to know if the fire was started deliberately, SBS reported.
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