Families were evacuated and smoke was billowing from a home in Sydney's west this afternoon as emergency authorities issued an urgent watch and act warning for the blaze.
The threat comes as temperatures soar in the New South Wales capital with the mercury expected to rise above 40C.
The NSW Rural Fire Service confirmed a fire was burning in bushland next to Whitehaven Rd in Northmead, with water bombing operations attempting to contain the spread.
Television images from ABC and Channel 7 shows at least one home impacted by the blaze, with multiple fire crews on the scene.
Residents are being urged to avoid the area and watch for embers that are threatening to start a fire ahead of the main blaze.
The fire threat comes as Sydneysiders endured the hottest November night since 1967, with the mercury not dipping south of 25.3C.
"Last night's minimum went down to 25.3 degrees at Observatory Hill," meteorologist Helen Kirkup told NCA NewsWire.
"Previously the highest November night on temperature was 24.8 degrees, which was in 1967."
For today, she said, the prediction was: "Just hot. Really hot."
The warm north-westerly wind will stick around and likely see the CBD hit 40C and Penrith 42C.
A cool southerly is expected to blow in between 2pm and 5pm, making for a far more comfortable evening.
Northeastern NSW is also facing a sweltering day, with Grafton expected to hit 42C and Taree 41C.
With temperatures expected to remain very high across the state in the coming days, NSW Health has urged people to cool their home through fans, airconditioning, closed blinds, and told to stay home.
"People going to the beach or pool should keep 1.5 metres from anyone other than those in their own household. To ensure everyone has an opportunity to enjoy the water and keeps out of the heat, we encourage people to swim and leave," the health department said in a statement.