Scorching heatwave conditions continue to grip much of Australia’s southeast, keeping authorities on high alert as fire conditions grow increasingly unpredictable.

Temperatures are expected to soar across parts of Victoria and South Australia on Tuesday, with the Bureau of Meteorology warning the extreme heat could break records.

Melbourne is set to swelter through its hottest day since the devastating Black Saturday bushfires in 2009, with a maximum temperature of 44C expected.

Melbourne skyline (file image)
Victoria’s capital is expected to hit 44C, while regional areas will also be blasted with heat. (James Ross/AAP PHOTOS)

Mildura, in the state’s far north, is forecast to reach 49C, while Broken Hill in NSW is expected to hit 47C, with both locations set to break temperature records.

“If Mildura does reach (that high), it will be the hottest temperature recorded in Victoria,” senior meteorologist Dean Narramore told AAP.

“Pretty much all observation points near the SA and Victorian border are either approaching or likely to exceed January records and a few locations could also break their all-time records.”

It comes as a total fire ban remain in place for both Victoria and SA as several fires burn out of control under dynamic conditions.

Records were broken on Monday in Adelaide where the temperature reached 44.7C, exceeding the city’s previous Australia Day heat record set in 2006.

Ceduna, northwest of the capital, climbed to 49C, surpassing its previous record temperature, while NSW town Dubbo reached 46.1C to record its hottest January day.

The weather conditions are worrying authorities in Victoria as multiple fires continue to burn out of control, including in the Otways where a blaze jumped containment lines at Carlisle River on Saturday, threatening the small community of Gellibrand.

Authorities say there has been unconfirmed property loss within the fire grounds.

Fire risk signage (fileimage)
Fire crews are on high alert as heatwave conditions bake much of southeast Australia. (Joel Carrett/AAP PHOTOS)

The bureau warns gusty southwesterly winds will hit Melbourne on Tuesday afternoon, with a risk of thunderstorms producing dry lightning.

A cooler change will begin to move through Victoria on Wednesday, although inland parts of the southeast won’t see much of a reprieve. 

Deputy incident controller Alistair Drayton says the gusty change is worrying, with authorities urging residents living in Gellibrand, Kawarren, Beech Forest, Forrest and Barongarook to evacuate. 

“The conditions tomorrow mean the fire could spread quickly and unpredictably. We strongly recommend people in affected areas to enact their bushfire plan, and leave early to protect themselves and their families,” he said.

An ambulance in Melbourne (file image)
Health authorities are urging people to drink plenty of water and stay indoors during the heatwave. (Michael Currie/AAP PHOTOS)

The heatwave conditions have also sparked a warning from paramedics, who responded to 11 cases of children locked in cars over the weekend as temperatures soared into the 40s in Victoria.

Ambulance Victoria urged the community never to leave children, pets, or older people unattended in vehicles.

“The temperature inside a vehicle can double and become deadly within minutes,” director of emergency management Dale Armstrong said.

“It is particularly dangerous for children to be left inside vehicles, as a child’s body temperature rises three to five times faster than an adult.”

Residents in both states are urged to drink plenty of water, check on family, friends, and neighbours to see if they need help and stay indoors.