THE mercury had almost reached 30C in Adelaide at just 6.30am as the nation's southern states prepared for a day of searing heat.Temperatures in the South Australian capital are expected to peak at 44C on Friday, with parts of the state set to swelter through a day in the mid-to-high 40s including 47C in Tarcoola and 46C in Port Augusta.
The Country Fire Service has declared a day of catastrophic fire danger for parts of the state.
Other southern states are also on high alert as Victoria faces a day of total fireban and crews in Tasmania continue to battle blazes that burned through the night.
Temperatures in Melbourne are forecast to hit 41C with the mercury climbing to 44C in Mildura and Ouyen.
The temperature in Hobart is forecast to reach 39C as fire crews continue to fight blazes around the state.
Just after 6am today, 21 fire fighting vehicles were battling a blaze at Lake Repulse.
A bushfire threatening the historic town of Richmond in Tasmania had been bought into containment lines by Thursday.
Early on Friday morning, nine fire fighting vehicles were at the sight where about 50 people had been evacuated on Thursday.
In Victoria, 8000 firefighters were at the ready.
Extreme fire danger ratings have been declared for the state's southwest, Wimmera, and Central regions on Friday while the rest of the state's danger rating is listed as severe.
Health alerts had been issued in SA and Victoria.
Adelaide's Central Bus Station will stay open around the clock to offer locals a place to cool down as the city swelters through a string of 40 degree days.
In Victoria, local governments have been preparing lists of vulnerable residents in a bid to minimise the risk to the elderly and those with medical conditions.
The effort comes after hundreds died in 2009 from the prolonged heat that occurred before the deadly Black Saturday bushfires.
Temperatures will remain above 40C for the next six or seven days in many inland parts of Australia.
Victoria is set to experience its longest stretch of heat and some of its worst fire conditions since Black Saturday when 173 people died.