Temperatures of over 40 degrees Celsius are forecast for large parts of Australia.
The ABC reports rural fire services in South Australia and Victoria are on high alert and residents in bushfire-prone areas are being urged to be prepared in case the worst happens.
A heatwave has already settled over northern parts of South Australia and the lower Northern Territory.
The temperature is forecast to reach 46 degrees at Tarcoola in the north-west of South Australia on Friday and 47 degrees on Monday.
Maximum temperatures at Roxby Downs are expected to range between 44 - 46 degrees for six days from Friday.
Adelaide is also facing 41 or 42 degrees for several days.
AAP reports many towns in eastern Western Australia and western Queensland will also feel the heat, with temperatures set to be in the 40s in parts of both states.
Even Hobart won't escape: 38 is predicted on Friday.
Victoria is preparing for one of the worst days since Black Saturday when 173 people died.
The ABC reports temperatures will rise into the 40s in the north of the state and are expected to stay that high until early next week.
However, there will be some relief for Melbourne and Hobart on Saturday due to a wind change.
"We're seeing the central Australia hot weather now moving into South Australia and Victoria,'' said Victoria Fire Services Commissioner Craig Lapsley.
''It will be around for a few days. Tomorrow we will see an extreme fire rating in SA and a severe rating for the Murray River, central Victoria, Melbourne and the west part of Gippsland."