Properties were under threat and residents told it was too late to leave as the fire burnt out of control at Tambaroora, about 270km north-west of Sydney.
Residents at Cranbrook near Dubbo were also under threat on Monday afternoon but an earlier emergency warning was downgraded to a watch and act.
About 48 homes were under threat by the blaze, which was sparked by a lighting strike.
The RFS said the fire was burning out of control in bushland north of Hill End and had crossed Alpha and Hill End roads.
Firefighters were working to protect nearby properties and continued through the night in the Lawlers Flat area to try to slow the spread of the blaze.
Late on Monday night, Firefighters reiterated calls for anyone near Sallys Flat, Maitland Camp and north of Doughertys Junction to leave now.
“If you are in the area of Alpha Road, Hill End Road, Ullamulla Road and Tambaroora, seek shelter as the fire approaches,” the RFS said.
“It is too late to leave. Go inside and protect yourself from the fire front. Actively monitor the situation.”
The RFS was expecting conditions to ease overnight but predicted a “prolonged firefighting effort over the coming days”.
Windy weather was making conditions more difficult for firefighters.
Earlier, an emergency warning was issued for the Cranbrook fire near Dubbo, about 400km north-west of Sydney, and a “shelter now” warning at nearby Toongi.
Just before 8pm, the warning was downgraded to a watch and act, with the RFS urging residents to monitor conditions.
The Cranbrook fire has burnt through 700 hectares.
There is also a watch and act warning for residents living in Burrendong, south-eat of Dubbo.
Sydney recorded its hottest day in more than two years on Monday, with temperatures set to remain hight into Wednesday.
RFS Commissioner Rob Rogers said earlier firefighters were worried because rain had caused vegetation to grow.
Rogers said parts of NSW haven’t had this level of fire risk in years.
“Before the 2019-20 fires, there was nothing out there because it was a drought and just dust,” he said.
“Now there is grass more than a metre tall and ready to burn and these fires move incredibly quickly.”
Tuesday should be hot again, heading for 34 degrees in the city.
Total fire bans will be in place for the Greater Hunter and Central Ranges areas.
