Overnight firefighters backburned along Heathcote Road near Pleasure Point as well as parts of the Holsworthy military base and, on Monday morning, crews were working to slow the spread of the fire.
"We had some very big fires here in 1994, we lost something like 20 homes", he said.
The flames briefly shut a section of the T8 train line, while several roads remain closed.
On Sunday, more than 500 firefighters in nearly 100 fire trucks, along with 15 aircraft, battled the blaze throughout the day.
The NSW Rural Fire Service has downgraded the threat level to "Advice", but urged residents to remain vigilant and to continue monitoring conditions.
The intensity of the blaze, fuelled by unseasonably hot weather and high winds, had alarmed firefighters.More news: Vincent Kompany delivers epic victory speech to Manchester City fans and players
"It is highly suspicious in the absence of any other cause like lightning".
"When you add on to that the unseasonably hot couple of weeks we came into autumn and into the month of April, we were talking about temperatures well and truly in the 30s (degrees Celsius), which were unprecedented", Fitzsimmons said.
"We don't tolerate this sort of thing".
"How dare anyone, if they are deliberately involved in lighting fires, endanger our firefighters and also putting all these communities in harm's way".
Waterbombers were on the scene throughout the afternoon, however windy conditions are hampering firefighters's efforts.
Local resident Jordan Dodin climbs onto a roof to protect the house from fire in Wattle Grove on Saturday night.More news: BCI asks Jammu, Kathua bar bodies to call off strike
NSW RFS Deputy Commissioner Rob Rogers said two giant aircraft, the DC10 Nancybird and the C130 Hercules "Thor" - normally used for aerial water bombing - were not available to help fight the Sydney fire.
"Still quite a hard day ahead (on Monday)", he told the Nine Network.
"I think we've got a long way to go before we're out of the woods", he said.
Authorities said wind speeds were not as severe on Monday, making it easier to battle the blaze.
The fire continues to burn in an easterly direction towards Barden Ridge, but the threat has been reduced.
Fire and Rescue NSW commissioner Paul Baxter said it was "remarkable" there had been no major loss of property, and said community co-operation with authorities had been invaluable.More news: Allardyce hails 'battling' Everton draw at Swansea
"They've been assisting the firefighters on the ground in that Heathcote Road area who will be doing what they can as the evening progresses to bring that fire under control".