The Bayindeen bushfire raging northwest of Ballarat has already burnt through more than 21,300 hectares, with forecast temperatures in the high 30s and wind gusts of up to 80km/h expected to fan the flames.

The danger is set increase from midday on Wednesday and authorities say the fire could rip through the communities of Beaufort, Elmhurst, Amphitheatre, Lexton, Learmonth and Clunes.

Residents have been warned to get out by Wednesday morning, while those in regions with extreme fire danger have also been told to flee.

Country Fire Authority chief Jason Heffernan asked anyone left in the area who is planning to defend their home to reconsider, as no houses are designed to survive catastrophic conditions.

“Unless your property is immaculately prepared and you have firefighting resources available, and that you are fit and mentally capable to sustain a long duration firefight in protecting your own home, my strong advice to community is leave early,” Mr Heffernan told ABC TV on Wednesday morning.

He said a cloud band over western Victoria had suppressed conditions during the morning but as soon as that breaks down scorching temperatures were set to kick in.

“Today unfortunately there’s real potential for thunderstorm and dry lightening as well, which could introduce further fire into the landscape,” he said.

The areas with an extreme fire danger rating on Wednesday are Mallee, Northern Country, North Central, Central and South West regions.

Mildura is set to reach 44C and other areas are also expected to creep into the 40s before a cool change in central parts of Victoria after 8pm AEDT.

Residents fleeing danger zones have been urged to go to built-up areas such as Ballarat, Ararat and Maryborough.

Victoria Police strategic commander Jason Templar told a Pyrenees Shire Council meeting at Beaufort on Tuesday afternoon rapid deployment teams would be ready to close roads at the incident controller’s behest on Wednesday.

“The messaging around being out and being out early is so important because once those roads close, that’s it,” he said.

“The reason we close them is purely for public safety, it’s too dangerous to be on those roads.”

Beaufort’s urgent care centre was closed on Wednesday and the Bayindeen bushfire threatened to cut power to homes if it came over the Western Highway.

About 500 firefighters were again expected on the ground, with more than 60 aircraft ready to fight the blaze and any fresh fires.

The NSW Rural Fire Service – which has deployed 25 fire trucks and 110 of its own firefighters to help battle the Bayindeen blaze – has additional aircraft on standby close to the Victorian border.

Extreme fire danger was also expected for much of eastern South Australia on Wednesday, with Emergency Services Minister Joe Szakacs warning the state’s firefighters were facing some of the harshest weather this summer.

Seven South Australian districts had an extreme fire danger rating on Wednesday.

“It’s entirely reasonable for the community to have enjoyed what has been some respite this summer, and we are days away from autumn,” Mr Szakacs told reporters.

“(But) complacency must be parked to the side. We are, as a state, facing some serious conditions.”

The Bayindeen fire in Victoria has destroyed six homes but more are expected to be accounted for once conditions subside.

More than 100 stock animals were killed in the fire or are missing, according to the State Control Centre.