Total fire bans are in place across 11 regions in New South Wales, while temperatures are forecast to soar in Sydney on Sunday with the mercury predicted to reach 40C in the CBD and western suburbs.
Bondi is tipped to reach 39C, while 40C is forecast in Paramatta, Blacktown, Canterbury and Campbelltown.
Residents in bushfire-prone areas in central and eastern parts of the state are being urged to review their survival plans, with the bushfire danger rating lifted to "severe" across much of New South Wales.
By 4:00pm, the temperature had climbed past 38C in the CBD.
Sea breezes often mean Sydney's eastern suburbs are spared the worst of the heat, and can often be 10 degrees cooler than non-coastal areas.
But on Sunday, things are different.
"That's because there is a front approaching and we've got really strong north-westerly winds ahead of that," BOM duty forecaster Rob Taggart said.
"Those winds will keep out the sea breeze.
"During the warm months, it will usually only happen a couple of times a year. During winter that is a lot more common."
The BOM said a late coastal southerly wind change will bring some relief to Sydney and surrounding areas.
The Rural Fire Service's Greg Allan said crews were on standby.
"Our crews have been aware that the forecast conditions today are going to be very hot and windy with those total fire bans in 11 areas so our volunteers as always are standing by ready to respond to fires when needed. Again, it's important to call triple-zero if you do see a fire," he said.
Josh Godden was one of the thousands of people cooling off at Bondi Beach.
"It's a beautiful day down here at North Bondi — I've spent most of the morning cooling off in the surf," he said.
"We're slip, slop, slapping to make sure we don't get burnt or overheat."ABC