Australians in Victoria have been warned they should prepare for 'property loss or worse' as much of the country faces extreme heatwave conditions. Temperatures on Friday and Saturday are forecast to hit record highs for most states and territories, with Victoria and South Australia in particular bracing for dangerous fire conditions due to strong winds and hot temperatures.

A total fire ban is in place in Victoria and all regions across the state were given a 'catastrophic' or 'extreme' fire danger rating.

Victorians should brace themselves for more property loss or worse, Country Fire Authority (CFA) chief officer Jason Heffernan told the Australian Broadcasting Corporation (ABC) on Friday.

The conditions were extreme yesterday. They're catastrophic today, Heffernan said. Temperatures in Melbourne are expected to hit 42C on Friday and while areas in north-west Victoria may reach 45C, a cool change is forecast in the south-west.

A bushfire near Longwood has burnt through nearly 36,000 hectares, destroying at least 20 homes in Ruffy. CFA captain George Noye said the town had been 'severely' affected, with significant destruction across the community.

In the Australian Capital Territory, a total fire ban was declared for the first time in six years. Sydney will see the mercury rise up to 42C on Saturday before dropping to around 26C by Sunday.

Authorities are also responding to other active fires throughout Victoria, with significant vigilance necessary for all residents as new fires emerge in the ongoing heat.