The fire, which started on Saturday afternoon, has burnt more than 2400 hectares and continues to burn in towards Barden Ridge.
Firefighters have worked overnight backburning around Voyager Point and Holsworthy.
Heathcote Road remains closed on Monday in both directions from Lucas Heights to Holsworthy.
"I can't believe homes were not lost in this fire," said RFS Commissioner Shane Fitzsimmons, praising the work of firefighters and residents who followed their bushfire survival plan.
"Yesterday we had over 500 firefighters working on the fire and that has been scaled down overnight to 250 firefighters still working on the ground," he told Network Seven.
Strong winds fuelled the blaze and burnt all weekend pushing residents and firefighters to their limits.
A strike force has been established to investigate the blaze which is believed to have started in Casula.
Water bombers are seen fighting a bushfire in Alfords Point as fire crews watch and wait in Sydney on Sunday.
AAP
"It is highly suspicious in the absence of any other cause like lightning. As we say all the time, no one tolerates this in the community," said Mr Fitzsimmons.
"We don't tolerate this sort of thing. It is irresponsible, criminal and how dare anybody if they're involved in this put the lives of firefighters at risk and all those communities that were in the path of this fire."
Conditions on Monday are expected to help the firefighting effort but winds could pick up to 35km/h later in the day.
Local resident Jordan Dodin climbs onto a roof to protect the house from fire in Wattle Grove on Saturday night.
AAP
But high temperatures remain a cause for concern, Rural Fire Service Deputy Commissioner Rob Rogers warned.
"Still quite a difficult 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."
The RFS cautioned that while the threat had eased, residents in the areas of Voyager Point, Pleasure Point, Sandy Point, Alfords Point, Barden Ridge, Illawong, Menai and Bangor should continue to monitor the situation and be
prepared to activate bushfire survival plans should conditions change.
RFS spokesman Greg Allan said on Sunday some properties had been damaged.
"We have had reports of impact on properties in west Menai and Barden Ridge but our crews at the moment are solely focused on fighting the fire," he told AAP.
The blaze was downgraded from watch-and-act to advice about 2am on Monday.
A large number of firefighters remain on the ground working to slow the spread of the fire.
