A home was lost at Marsden Park, in Sydney's west, on Tuesday, in one of the earliest starts to a bushfire season in a long time.
The RFS hasn't ruled out that the fires were deliberately lit or were the result of backburning. But Mr O'Farrell said backburning was an essential part of preparations for summer.
"We are deliberately encouraging as much hazard reduction as possible," he told reporters in Winmalee on Wednesday, about half a kilometre from the front of one of Tuesday's biggest blazes."When you don't undertake hazard reduction you leave the fuel load as it is and it grows and that's even more lethal."
He urged residents in bushfire prone areas to undertake "additional responsibilities" in the lead up to the summer months.
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"They need to take additional fire protection measures, they need to clean up around their properties, they need to clean their gutters," he said. "It's clearly going to be a difficult bushfire season."
Mr O'Farrell also paid tribute to firefighters - paid and volunteer - who were battling bushfires in Sydney's west.
RFS Commissioner Shane Fitzsimmons said there were about 60 fires still burning across NSW, with 25 of them uncontained.
He said a blaze near Marsden Park in Sydney's northwest was under control, adding he was optimistic fires near Londonderry and Windsor Downs would be contained later on Wednesday.
He said fire crews at Winmalee would be working 24 hours a day to bring that fire under control, an effort that could take "many days".
