Residents in the suburbs of Voyager Point, Pleasure Point, Sandy Point and Illawong, Menai and Bangor were warned of the danger of ember attacks as many scrambled with hoses and buckets to protect their houses.
The 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.
Many residents in Menai chose to remain at their homes and were kept busy fighting ember attacks.
Local MP Craig Kelly said because most of the communities in the area were quite bushy and remote, residents understood the risk of bushfires.
"That is a huge relief", she told reporters at the RFS headquarters in Sydney.
"We believe it might have been a deliberately lit fire", Inspector Mitch Newtown said on Saturday night.
On Sunday, more than 500 firefighters in nearly 100 fire trucks, along with 15 aircraft, battled the blaze throughout the day.
NSW Police on Sunday evening announced a task force had been set up to investigate whether the fire, which began in the vicinity of Leacocks Reserve in Casula, was deliberately lit.
Hundreds of people were evacuated from their homes on Saturday night, with the flames burning within metres of properties in Holsworthy and Wattle Grove.
The fire resulted in hundreds of people being evacuated from their homes on Saturday evening with flames nearly reaching properties at Holsworthy and Wattle Grove and spot fires later threatening Sutherland and Menai.
Mr Fitzsimmons on Sunday morning stressed the fight wasn't over saying "there's still a long way to go this afternoon".
There's no immediate concern for the Lucas Heights nuclear reactor but authorities are prepared if the facility is threatened, the RFS commissioner said.
The NSW RFS has reduced the threat level to "Advice" as fire crews continue to battle the blaze.
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