Out-of-control bushfires continue to rage across across Victoria, including the Grampians in the state's west, which has burnt more than 41,000 hectares, Bullengarook in Melbourne's northwest, and the Gurdies in western Gippsland.
But conditions are set to intensify across the state when temperatures reach into 40C on Boxing Day, fanned by strong and dry winds, Victorian Emergency Management Commissioner Rick Nugent said.
"We have some very difficult weather conditions on Thursday and Friday," he said.
"These conditions will make it far easier for fires to start and to spread and for existing fires to race off in the direction of the wind."
Elsewhere in NSW, several small bush and grass fires have continued to burn across parts of the state but remain under control.
The fire risk set to ease in the lead-up to Christmas before a significant part of the state faces high fire dangers on Boxing Day.
South Australian firefighters urged residents to leave in the Onkaparinga Hills in the Mount Lofty Ranges as they battled an out-of-control bushfire on Monday afternoon.
They later downgraded their warning, telling residents to monitor conditions.
Regional areas across the state are expecting hot conditions on Boxing Day, with Adelaide facing a peak of 36C after a predicted 37C on Christmas Day.
Victorian bushfire have the potential to worsen amid extreme hot weather on December 26. (HANDOUT/STATE CONTROL CENTRE)
Firefighters in Western Australia on Monday night upgraded a bushfire alert, warning residents it was "too late to leave" as a blaze intensified around 100 kilometres northeast of Perth, near the wheatbelt town of Northam.Â
Fires already burning across Victoria have the potential to worsen as extreme hot weather blankets most of the state on December 26, leading to authorities pleading with travellers to reconsider their trips.
"Our state will have all areas ... in extreme fire danger rating, except for East Gippsland on Thursday," Mr Nugent said.
Country Fire Authority chief executive Jason Heffernan urged those who can avoid travelling through those areas during the Christmas break to do so.
"If you do have to travel, have the VicEmergency app, you need to know where you're going, and you also need to have that information available to you to be situationally aware," he said.
About 100 fire personnel from NSW, the ACT, Queensland and Tasmania are set to arrive in Victoria to help battle the blazes.
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