Temperature records have been smashed in Sydney as the city swelters through its hottest October day on record.
The mercury reached 35.6C at Observatory Hill just after 3.30pm on Sunday while Penrith in the city's west was even hotter, with the temperature hitting 37.3C just after 3pm.
The previous record October temperature was 33.1C at Observatory Hill on the same day in both 1961 and 2009, Bureau of Meteorology data showed.
Beaches, pools and riverways across the state were packed as holiday-makers made the most of the long weekend and cooled off.
Inland areas of NSW were just as warm as the coast, with the mercury hitting 38.5C at Bourke, in NSW's upper west.
Temperatures in the mid to high 30s were recorded on the south coast, with wind warnings leading to nine fire bans across the state.
Five separate regions have been declared at extreme risk of fire, with high temperatures, strong winds and low humidity.
Strong northwesterly winds were felt along the Snowy Mountains and the south coast, the Southern Tablelands, southwest slopes and the ACT.
The NSW Rural Fire Service (RFS) has declared a total fire ban for the state's southwest for Monday.
It said 75 fires were burning across the state on Sunday, 30 of them uncontained.
RFS Commissioner Rob Rogers said authorities were doing everything possible to protect the community but called on families to brush up on their bushfire survival plans.
"It's no good just mum or dad knowing it because if they're not there, everybody else needs to know what to do," he told reporters.
A cool southerly change is expected to blow up the NSW coast late on Sunday night, with southern states already experiencing a major drop in temperatures.
Adelaide reached 32C on Saturday but the temperature on Sunday was significantly cooler, in the low 20s.
The strong winds have sparked raging fires and emergency warnings in eastern Victoria.
An out-of-control fire is burning north of Maffra in the Gippsland region, with people in Briagolong, Culloden, Moornapa, Stockdale and surrounds initially told to evacuate.
"If you are camping in the area, evacuate immediately," a VicEmergency alert said.
"This fire is currently travelling in a south-easterly direction."
About 70km southeast, residents were told to immediately shelter indoors as an emergency-level grass fire swept across the coastline.
The fire was about 4.2km southwest of Loch Sport on Sunday and moving in an easterly direction.
A third emergency warning issued earlier for a grass fire further west at Forge Creek has been downgraded.
Wind gusts of more than 100km/h were recorded in parts of west and south Gippsland on Sunday as the mercury dipped below 20C.
The CFA has declared a total fire ban for Monday for the Mallee in the state's northeast.
In Tasmania, a watch and act alert has been issued for an uncontrollable bushfire at Boat Harbour Creek on Flinders Island.
"Embers, smoke, and ash may fall on Leeka and West End Road and threaten you and your home before the main fire arrives," the alert said.
Queensland Fire and Emergency services have been battling blazes from Townsville down to the Gold Coast, with 10 at advice alert level.
High fire danger ratings have been enacted in 18 weather districts across Western Australia as several fires burn at advice levels.
