There are fire bans across large parts of Victoria and South Australia, with temperatures expected to top 40 degrees.
Fire authorities are urging residents in Victoria's north and west to enact bushfire survival plans, and a total fire ban has been declared for the Mallee, North Central, Northern Country, Wimmera and South West Districts.
Fire bans have also been put in place across nearly all of South Australia, which is facing similarly dangerous conditions, and in the Southern Riverina district of New South Wales.
Country Fire Authority State Duty Officer Peter Baker says there is a high risk of grass fires across Victoria.
"Across pretty much all of Victoria, except for the eastern and southern Gippsland parts, the grassland is extremely dry," he said.
"We've got winds from the north, so they're hot winds. They will be up around anywhere between 25 and 50 kilometres per hour depending where you are.
"With the heat ... that's a recipe for fire."
Mr Baker urged any holidaymakers travelling through unfamiliar territory to be aware of the risks.
"There's a whole bunch of people travelling across Victoria at the moment who aren't necessarily familiar with the local conditions," he said.
"For those people we would say check the website, go and talk to local people about what do do."
Senior weather forecaster Terry Ryan says hot and windy conditions are expected across Victoria, particularly in the state's north and west.
"Mainly the grasslands are affected this time," he said.
"The grass has dried out a lot. They're cured and ready to burn, basically."
South Australia's Country Fire Service (CFS) has issued a fire ban for all districts except the North East Pastoral, and is warning of extreme bushfire danger in a number of districts including the Adelaide Hills.
Extreme fire danger ratings have been issued for the Mount Lofty Ranges, Yorke Peninsula and Lower South East.
SA Power Networks spokeswoman Sue Filby says people need to take precautions in hot weather because there is the potential for the power to be switched off.
"We monitor very closely the change of conditions over the state, and if the circumstances so require, we will disconnect power where there is a risk to lives and property," she said.
"People can lose power at any time, but in bushfire-risk circumstances we do take our responsibilities very seriously, and we try to respond to any changing risk when it's at the extreme or catastrophic level."
This latest heatwave comes as Victoria's fire authorities unveil a high-tech weapon to help them in the fight against bushfires.
The program, developed by the University of Melbourne, can plot the behaviour of a bushfire over a two to six hour window, only minutes after it first breaks out.
Victoria's Fire Services Commissioner Craig Lapsley says the technology lets controllers share the most up to date information with those in the field
"If you don't have the timely information you can't make good decisions," he said.
"This will be one of the key tools we'll use, and use effectively.
"It's all about community consequence - where is this going to impact on a community, how do we get our message right, what do we need to tell them, in what time [and] circumstances.
"It's absolutely fantastic for firefighters to have that, or the managers of the fires to have it, but it's critical for us to advise our communities of where the fires are."
Fire behaviour analyst Jamie Norris says the system is accurate and fast.
"It's looking at fuel types, it looks at the weather information, and it also looks at topography," he said.
"You used to have to use a ruler and a crayon to identify the path of a fire."
The technology was created about two years ago, but with seasons of low fire danger, it hasn't been used before this week.
© ABC 2012
13:37 EST A hail storm barged through Sydney yesterday afternoon, bringing 1-2 cenimetre-sized pellets and heavy downpours, effectively turning summer into winter.