If a huge bushfire in Sydney's southwest on the weekend was deliberately lit, as authorities suspect, it's a "sickening and reprehensible" act of arson, the NSW Rural Fire Service commissioner says.
Fire investigators are working with NSW Police's Strikeforce Carpi to determine the cause of the blaze which started on Saturday at Casula and is being treated as suspicious
Detectives want to determine if there is a link to several spot fires in the Leacock Reserve area on Friday night.
Less than 24 hours later a bushfire flared up about 2.30pm on Saturday in the same area.
It's now burnt through more than 2400 hectares of land and come dangerously close to homes.
"The area where we believe the fire commenced has been forensically examined," Acting Superintendent Paul Albury told reporters on Monday.
"We have taken a number of statements from people who called the police and fire services in regards to the fire."
It's unclear if Friday's fires reignited on Saturday or if someone may have deliberately lit the next day's blaze which then ripped through much of the Holsworthy military range.
Act Supt Albury said it was too early to identify who could have been responsible but noted it might have been a local.
"It's certainly a line of inquiry given the remote nature of the reserve - that somebody locally may have been involved," he said.
He described the reserve as a "dense level of bushland" near Casula train station and the Georges River.
It's a "well known local reserve" used by residents for walking and bike riding, he added.
But in terms of potential witnesses he said: "You're talking about 10pm on Friday night in a densely bushed area."
"There is no lighting, there is no CCTV footage and there were limited people walking in that area at that particular time."
The area has been forensically examined and detectives are combing through CCTV footage from the nearby station.
They are also speaking to a woman who was on a platform when Friday's fires started.
RFS Commissioner Shane Fitzsimmons slammed the alleged firebug, saying any such act would be "sickening and reprehensible":
"How dare anyone in society think they can deliberately light a fire, endanger all these men and women - the vast majority who are volunteers - putting their lives on the line to try and bring these fires under control and, in turn, put so many members of the community (at risk)," the commissioner said.
Mr Fitzsimmons noted it was potentially "a very serious crime" with NSW having the toughest penalties in Australia.
Offenders can face hefty fines and up to 25 years in jail, he said on Monday.
The Casula Powerhouse Arts Centre, which is next to the reserve where the fire is believed to have started, had a close call on Saturday night, its director Craig Donarski said.
"The footage on television made it look apocalyptic," he told AAP.
"We were very lucky, what was happening around here seemed light but what was happening across the river was gnarly."
Mr Donarski said the area was popular with locals and kids during the day but didn't attract many people at night.