The highest level Code Red catastrophic fire alert has been declared for Victoria's north country and north east regions today.
Lightning strikes pose the greatest risk of sparking bushfires this evening, with thunderstorms already moving across from the west.
Today was the state's first ever catastrophic fire day with a code red issued for the Wimmera under the new rating system.
Country Fire Authority chief Russell Rees says people in the north country and north east, with temperatures forecast to be above 40 degrees, should leave tonight or early tomorrow.
A total fire ban's been declared in the North Western, North Eastern, Eastern and Central districts.
Extreme fire danger ratings are declared in the North Central and the Mallee.
South Australia concerns
Firefighters in South Australia have been tackling an out-of-control blaze between Mount Pleasant and Tungkillo.
Local residents were advised to leave, but firefighters say the risk has now reduced.
The Country Fire Service in South Australia has also issued fire bans across the state for tomorrow.
Earlier strong winds and temperatures soared into the low 40s Celsius, but a cool change is expected to sweep across the state overnight.
Bracing for the worst
Meanwhile, NSW firefighters are also bracing for the worst tomorrow, with temperatures set to soar into the 40s across many parts of the state.
Strong winds, low humidity and high temperatures are forecast.
Rural Fire Service Commissioner Shane Fitzsimmons said those under threat should make plans to leave early.
"Under these conditions, fires that start and take hold will typically be uncontrollable and potentially dangerous," he said.
"It's critical that people, especially across southwestern and southern NSW, are alert to the potential for fire activity and ensure they have a plan for what to do if a fire affects the area they're in."
A catastrophic fire danger rating has been declared in the Northern Riverina, Southern Riverina and southwestern areas of NSW.
Total fire bans are in place in the Southern Ranges, the Lower Central West Plains, Monaro, the Southern Slopes and the Eastern, Northern and Southern Riverina districts.
A total fire ban has also been declared in the ACT and in the Northern and Southern regions of Tasmania tomorrow.
