A massive bushfire could break containment lines and start burning through suburban areas of western Sydney if conditions deteriorate, firefighters have warned.
NSW Rural Fire Service Commissioner Shane Fitzsimmons says the 264,000-hectare Green Wattle Creek bushfire on Sydney's southwestern outskirts is a priority on Saturday.
"There is potential for the fire to break out, cross the (Warragamba) dam and move into the western suburbs of Sydney," he told reporters on Saturday morning.
"It has the potential to come out into more populated areas this afternoon."
Mr Fitzsimmons said crews have been working around the clock to contain the Green Wattle Creek blaze.
"Crews have been doing extraordinary work with backburning and the use of aircraft and machinery on the ground to try and lock that in," he said.
"That's one of our focus fires, of course, but I would say as a broader message be alert, be focused on any new fires today."
Extreme fire danger is forecast for six fire districts in NSW's southeast and the ACT, while severe conditions are forecast for Sydney, the Hunter and the central ranges.
There are some 137 bushfires burning in NSW on Saturday morning, with around 60 uncontained.
More than 3000 firefighters are on the frontline, with 31 specialist strike teams in place across NSW.
Fire conditions to ramp up in south NSW
Many residents on the NSW south coast are taking refuge in evacuation centres ahead of forecast dangerous fire conditions.
Northeasterly and westerly winds are forecast throughout the day with a southeasterly wind change expected late on Saturday afternoon.
NSW Rural Fire Service assistant fire behaviour analyst Andrew Nicholls said conditions are expected to rapidly change throughout the day.
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"Fire conditions are going to ramp up really quickly," he told AAP in Moruya.
"The difference between 9am and 11am will be huge,” he added.
The southeasterly change is due to come in from 5pm in Narooma, 6pm in Moruya and 8pm in Nowra.
"It'll be something like 30km/h and there will be some areas that will gust at 50km/h," Mr Nicholls said.
Hot temperatures into the 40s are forecast but a thick blanket of smoke might bring temperatures down, he said.
"There is such a thick blanket of smoke it might take down the temperatures from 43C back down to 38 or 35C."
Residents from Bega to Nowra have heeded messages from emergency services and many have taken refuge in evacuation centres in major towns along the coast.
For more advice on bushfires in your area head to the NSW RFS Fires Near Me page.
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