Dangerous fire conditions are set to sweep across several states as the south-east braces for a Boxing Day scorcher.

Damaging winds will fan extreme fire danger on Thursday as hot and dry weather envelops large parts of Victoria, south-west New South Wales and much of eastern South Australia.

The mercury is set to reach the high 30s to 40s for much of Victoria and inland Australia, with the central western Queensland town of Birdsville forecast for a 47C belter.

Gusts of up to 100km/h are strong enough to bring down trees and power lines, and cause minor power outages, the Bureau of Meteorology senior forecaster Dean Narramore said.

A high-pressure trough which brought temperatures in the high 30s to South Australia on Christmas Day is slowly trekking across the border to Victoria.

All but one region of Victoria are set to face extreme fire risk on Thursday.

Total fire bans have also been declared for South Australia’s Mid North, Riverland, Murraylands, Upper South East and Lower South East regions.

The dangerous conditions could further fuel an out-of-control bushfire in Victoria’s Grampians National Park which has been burning for days, covering more than 40,000 hectares.

Victoria State Control Centre spokesman Luke Hegarty warned people in the Grampians, The Gurdies, Bullengarook, and Creswick to prepare their bushfire survival plans.

“If you choose to leave these areas of elevated risk, go on the night of December 25, or no later than 10am on December 26, before the extreme fire danger conditions begin,” he said.

Residents in the Grampians towns of Bornes Hill, Moyston and Pomonal were also ordered to leave on Wednesday as the blaze raced towards them.

Narramore said the combination of strong winds, high temperatures and dry air made for dangerous fire activity.

“Any fire that does get going or already is ongoing around the Grampians will likely be uncontrollable and uncontainable, leading to dangerous and erratic fire behaviour,” he said.

Firefighters from multiple states have deployed to help their Victorian counterparts as crews work to secure containment lines on Boxing Day which is expected to bring the worst conditions since the 2019 Black Summer.

Power provider AusNet warned customers that power cuts could be triggered to prevent bushfires from starting and outages could last longer to ensure safety.

As a cool change washes over Victoria on Thursday night, hot, dry and windy conditions will push into parts of central north-eastern NSW, bringing extreme fire danger on Friday.