Two states are bracing for "uncontrollable" bushfires with the risk of dry lightning and a gusty cool change, as temperatures hover around 40C.
There is an extreme fire danger for western and central Victoria and much of eastern South Australia on Monday afternoon, prompting total fire bans across high-risk areas.
In Victoria, the CFA issued a "leave now" alert for visitors and campers in the Little Desert National Park because of multiple fires.
A "leave now" alert was also issued for Barunah Park, Corindhap, Rokewood, Shelford and Warrambine in response to a grassfire at Rokewood that was not yet controlled.
The combination of hot, dry, windy conditions and dry lightning, meant fires would be uncontrollable and lead to dangerous and erratic behaviour, Bureau of Meteorology senior meteorologist Dean Narramore warned.
"These hot, dry and northerly winds are likely to lead to temperatures 12 to 14C above average for this time of year, and dry lighting also likely to develop on and ahead of the change," he said.
Temperatures in northern Victoria and some regions of NSW had soared into the low to mid 40s by late afternoon.
Sydneysiders flocked to the beach on the public holiday to cool down.In South Australia, police and CFS responded to a grass fire at Panorama, near Blackwood in the Mt Lofty Ranges, containing the blaze without the loss of any property.
A grass fire at Kanmantoo in the Adelaide Hills was also contained and in the Barossa Valley, CFS crews were responding to a grassfire at Rowland Flat.
Southern Tasmania is also under total fire ban with hot and windy conditions.
Amid the hot, dry weather, Adelaide has fired up its desalination plant after the lowest inflows to the city's reservoirs in 40 years were recorded in 2024.
It was Adelaide's driest year since 2006, with only 347mm of rain over the 12 months, nearly 200mm below average.
Combined reservoir levels are at 44 per cent, the lowest level for more than 20 years, but Adelaide's water supply would remain secure, with enough to meet the needs of the community, Housing and Urban Development Minister Nick Champion said.
The desalination plant will temporarily produce up to 300 million litres of water per day during February and the city would otherwise face water restrictions.
"If we didn't have this plant, I would be having sleepless nights," Mr Champion said.
