An emergency warning was issued on Friday afternoon for residents in Mafeking and Watgania to leave immediately as the blaze in western Victoria's Grampians National Park intensified.
Those in nearby Bornes Hill, Grampians, Jimmy Creek, Mirranatwa and Victoria Valley should prepare to leave, emergency services said.
About 300km to the southeast near Phillip Island, locals in The Gurdies, St Helier and Woodleigh have been urged to take shelter as a fire there grows and pushes eastward.
"It's too late for people in that area to leave," State Control Centre spokesman Luke Hegarty said.
"They should take shelter now indoors if they are still in the area."
The Grampians fire has grown to at least 12,000 hectares after being sparked by a series of lightning strikes on Tuesday.
Huge columns of smoke have impeded visibility and created dangerous turbulence for aerial water bombers, Mr Hegarty said.
An emergency relief centre has been set up at Alexandra Oval in Ararat.
The fire in Victoria's west was expected to burn for weeks to come.
A cool front moving across the state is expected to ease temperatures but will bring little rain.
High fire danger is expected to persist in western, northwest and northern Victoria into next week, and the risk in Wimmera and Mallee districts will be downgraded from extreme to high from Saturday.
After some areas climbed above 30C in the state on Friday, temperatures in the Grampians were forecast to ease to 20C on Saturday.
The Grampians fire has sparked raft of tourism cancellations at the popular camping and hiking destination.
South of the bushfire, Dunkeld Caravan Park caretaker Erin Hinchliffe said the campsite remained open but only four sites were booked following 30 cancellations.
"We're starting to get a little bit on edge because of not knowing what's actually going to happen with the weather patterns today," she told ABC Radio Melbourne.
"We had a full house. It was the first time in six years that we've been able to get the occupancy up over Christmas and New Year period."
Emergency Management Victoria controller Mark Gunning said the area around the fire, which started near Yarram Gap Road, was already extremely dry and very little rain was forecast.
"It is in really challenging country, which has allowed the fire to establish on the escarpment," he said.
Two air tankers have been continuously water-bombing the fire, assisting a significant deployment of the state's aerial firefighting resources.
Some roads and areas of the Southern Grampians are closed but large, popular tourist sections of the national park remain open to visitors.
