MUCH of country Victoria and South Australia is facing a total fire ban with the temperature tipped to reach 39C.
The Country Fire Authority has declared a total fire ban for the Mallee, North Central, Northern Country, Wimmera and South West districts tomorrow.
No fires can be lit in the open air between 00:01 and 23:59 (AEDT) on Sunday, the CFA says.
"The CFA advises people living in areas at risk of fire to activate their bush fire plan," it said in a statement today.
The Bureau of Meteorology expects a very hot day statewide, with a gusty cool change set to arrive from the southwest in the afternoon.
Milder weather is on the way for Christmas Eve and Christmas Day, with possible early showers to give way to maximum temperatures of 26C and 22C respectively, the BOM says.
Much of South Australia will also be on total fire bans, with soaring temperatures tipped to reach 39C.
The Country Fire Service has said 13 districts face an extreme or severe risk of fire on Sunday and declared a 24-hour total fire ban from midnight.
The affected districts are Northwest Pastoral, West Coast, Eastern Eyre Peninsula, Lower Eyre Peninsula, Flinders, Mid North, Mount Lofty Ranges, Yorke Peninsula, Kangaroo Island, Riverland, Murraylands, Upper South East and Lower South East.
The CFS is urging the thousands of affected residents to ready their bushfire plans.
"If you don't have a plan to ensure your survival, leaving early before a fire starts is your safest option," it said in a statement.
The Bureau of Meteorology says the searing heat will continue across the state until a late Sunday afternoon change.