A total fire ban has been issued for the greater Sydney region after the city sweated through its hottest day in almost 80 years.
Penrith, in the city's west, exceeded 47 degrees Celsius on Sunday afternoon but conditions across the city cooled slightly on Monday morning with some early rainfall.
Temperatures in the city on Monday will sit in the mid 30s but the mercury in the city's west will hit the 40s, according to the weather bureau.
Rural Fire Service (RFS) spokesman James Morris has warned the public against becoming complacent about the risk of fires.
Monday's forecasted winds and rainfall won't penetrate too far west, with Penrith and Richmond still expected to reach up to 40C while parts of the Hunter Region brace for temperatures up to 43C, he said.
"That's accompanied by winds which may push up around the 40-kilometre mark, so firefighters are on standby to respond to anything should it kick off," Mr Morris told ABC Radio on Monday.
"We've seen over the past month, fires that we've had haven't necessarily been burning on days of severe or above-fire-danger rating ... the fuel is dry out there, the fuel's dry all around NSW."
More than 50 new fires were sparked on Sunday, with 21 blazes continuing to burn into Monday, according to the RFS, and a severe fire danger rating was issued for the Hunter region.
Sydney was reportedly the hottest place on earth on Sunday with Penrith taking out the title of the hottest part of the city on Sunday, reaching 47.3C just after 2.30 pm.
Richmond reached 46.3C just after 2.30pm while the temperature in Bankstown broke 45C.
The NSW Rural Fire Service warned residents to prepare their bushfire plans. If people are considering leaving their homes they should "leave early", the RFS said.