AS ADELAIDE sweltered through 45C yesterday, some regional centres have felt the heat at even more uncomfortable levels.

In Victoria, Avalon recorded 42.1 degrees at 10.32am, while Geelong peaked at 41.7 at 10.35am, according to the Bureau of Meteorology.

In the state's west, Mortlake, Hopetoun, Horsham, Nhill and Longerenong had all reached 40 degrees by 11.00am.

Aireys Inlet, Port Fairy, Warrnambool, Yarram and the Latrobe Valley have also reached 40 degrees.

South Australians are also sweating through another day of extreme heat, after the mercury peaked at 45.7 degrees in Adelaide yesterday.

The temperature has already reached 39.8 in Adelaide today, and broken the 40 degree barrier at Edinburgh, Keith, Padthaway, Naracoorte and Coonawarra.

Forecasters are tipping most of southeast Australia will experience 40+ temperatures today, after sweltering through searing temperatures yesterday and overnight.

Mallee towns Hopetoun, Longerenong and Nhill all peaked at 45 degrees yesterday.

Mildura and Swan Hill baked at 43.7 degrees and 42.8 degrees respectively, while Melbourne recorded a 43.4 degree stinker.

Victoria's 100,000 firefighters are on red alert, as strong winds combine with extreme heat today.

Total fire bans are in place across the state.

CFA state duty officer Alan Ellis said strong, dry winds would "absolutely make things difficult'' for firefighters.

"We are expecting 35 to 40km/h winds at Ballarat and near Melbourne, which is up quite a bit (from Wednesday),'' Mr Ellis said.

Fire crews worked hard to control a grass fire at McCrae on the Mornington Peninsula yesterday.

Four firefighters were treated for smoke inhalation after the 4ha blaze burnt through tea-tree and scorched back fences.

Overnight, fire crews contained a 30ha fire burning in bush on private land at Delburn, south of Morwell in the Latrobe Valley.

A fire that destroyed 20ha of farmland, a shed and hay bales near Winchelsea, in the state's south-west, was contained with the use of water-bombing helicopters.

Emergency Services Commissioner Bruce Esplin urged Victorians to look out for neighbours during the heatwave, to ease pressure on emergency services.