South Australia is bracing for bushfires over the festive season, with authorities predicting the most dangerous Christmas Day fire conditions in decades.
The mercury is set to reach 37C in Adelaide on Friday, with strong northerly winds forecast throughout the morning.
A significant change is tipped to arrive mid-afternoon, bringing cooler temperatures but also very gusty southerly winds and possible lightning storms.
Total fire bans are expected to be issued in up to 10 districts and firefighters will be on standby across the state to deal with any flare-ups.
Country Fire Service state coordinator Leigh Miller says the forecast conditions are the worst he can recall for Christmas Day in almost 30 years.
"We don't need to have catastrophic conditions for bad fires to start," he told reporters.
"We've had many fires continue, throughout all the years we've been in the CFS, in conditions much less than what we're going to be facing on Christmas Day."
Bureau of Meteorology acting regional director John Nairn said Friday's forecast cool change should not be cause for complacency.
"What we're likely to see is that the most dangerous fire conditions are after the change comes through," he said.
Adelaide's temperature is set to reach 38C on Christmas Eve, with total fire bans declared in the west coast, lower south east and eastern Eyre Peninsula districts.
Hot and dangerous conditions expected in Victoria
It will get tougher for firefighters on Christmas Eve, with hot, windy weather forecast and fires burning close to Victorian towns, including Lorne.
Hot and dangerous bushfire conditions are expected in parts of Victoria on Christmas Eve where firefighters are working frantically to control blazes.
Two bushfires are yet to be contained and the drier than usual year and tinder dry bushland is making it difficult for firefighters.
That includes a fire 8km west of Lorne on the Surf Coast, dotted with holiday houses and with thousands of motorists heading down the Great Ocean Road for breaks over the Christmas and New Year period.
About 100 firefighters, five aircraft and nearly 30 trucks have been sent to the large Jamieson Track near Lorne in the Great Otway National Park.
A bushfire raging over 7700 hectares near Barnawartha in the state's northeast, which has claimed four homes, also remains out of control with 18 houses in total lost in Victorian fires in the past week.
Temperatures will be well above 30C on Christmas Eve and Christmas, and wind gusts of up to 45km/h will create highly dangerous fire conditions across the state.
Victoria's fire commissioner Craig Lapsley says a severe fire warning has been issued for the southwest, Wimmera and central Victoria districts in the next few days.
"Christmas day will be a hot day, a windy day ... and this means if a fire starts, it can run fast, it will be intense and it will change direction with the wind change," he told reporters on Wednesday.
The Great Ocean Road remains open.
Lower temperatures and substantial rain are expected to hit Victoria on Boxing Day.
