Wilcannia Airport in north-western NSW has already hit 46.3 degrees Celsius today with a forecast top of 48C.

At noon, Fowlers Gap and White Cliffs Airport were not far behind, recording temperatures over 45C.

Wentworth is expected to reach 49 while Ivanhoe is also forecast to reach 48C.

Trangie Research Station along with Dubbo and Mudgee airports broke January records yesterday.

In Trangie, temperatures reached 47.3C for the first time in January in the 58 years since data has been collected at the location.

Meanwhile, Dubbo reached January records of 46.1C and Mudgee 42.9C.

Bureau of Meteorology senior forecaster Chrisie Johnson said overnight temperatures offered little relief for some places in the far west.

"Broken Hill stayed just around 30 degrees overnight and Tibooburra did not even get below 31," Ms Johnson said

"We're looking at another hot one today.

"The peak of the heat is going to be migrating back out into the far west."

Two relief centres are operating in the Victorian town of Colac, with the CEO of Colac Otway Shire encouraging people in the area to make their decisions early.

Speaking on ABC Radio this morning, CEO Andrew Tenni says he is worried about people "leaving it late".

"Then we've got a big choke-up in town with people trying to get into those relief centres," he says.

"We'd encourage people to make their decisions early and try and get to those centres so we can get them organised as soon as possible."

About 35 people were at the Colac Showgrounds this morning, which is running around the clock, and welcoming caravans, pets and livestock.

"We've got around 20 dogs and even six sheep out there at the moment," Mr Tenni told the ABC. 

About 14 people were at the second relief centre at Bluewater Leisure Centre earlier this morning.

But Mr Tenni said they were expecting a "large influx" of people at both centres throughout the afternoon.

In Central Australia, 40 degrees Celsius plus days aren't an uncommon sight during the summer, but that doesn't mean they should be taken any less seriously.

Severe heatwave warnings remain in place for the Simpson and Lasseter districts today, including Alice Springs and Yulara, with temperatures set to reach the low 40s in those areas. 

The remote community of Apatula / Finke is forecast to be the hottest place in territory today with a top of 44­C.

Thankfully, those conditions are expected to ease as the week goes on.

A cool change is starting to flow through in Adelaide, where the temperature peaked at 42.2 degrees Celsius just before 11am and has since fallen back to 37.8C.

Ceduna is on 26.7C — about half the record set in the far west coast town yesterday.

Bureau of Meteorology meteorologist Jonathan How says winds have turned from northerly to south-westerly.

"Across Adelaide, we'll gradually see those temperatures falling through the afternoon, but [it is] very hot away from the cool change — it's already hit 45–46 degrees in the Murraylands and also temperatures [are] reaching the mid-40s across further northern parts," he said.

"So, with that wind change coming through, it will be a bit gusty, and so that will really create some challenging fire weather conditions again.

"We're expecting extreme fire weather conditions and just no rainfall with this cool change coming through."

In addition to the Emergency Warning just announced, there are a number of Watch and Act warnings for towns surrounding the Carlisle River fire.

The three regions to the south and the east of the fire, which includes Forrest and Beech Forest, are under a Watch and Act have been told to evacuate immediately.

The wider warning area, which encompasses popular coastal towns along the Great Ocean Road like Lorne and Apollo Bay, have been told to monitor conditions.

Authorities expect the fire to grow quickly today amid hot temperatures and a gusty wind change expected about 5pm.

Here's where the fire is in relation to Melbourne:

The temperature in Melbourne had already passed 34 degrees Celsius by 11.30am on its way to a predicted top of 45C today.

Many people took to the beach to escape the heat.

The Bureau of Meteorology was predicting temperatures to steadily climb and peak about 5pm today before a cool change.

The mercury is forecast to drop to about 32C by 10pm, but temperatures will stay in the mid 20s overnight.

Craig Vermay is from Barongarook West, near the Carlisle River fire in the Otways. 

He and his neighbours have been on high alert, with people evacuated from nearby areas. 

Craig told NewsRadio's Sarah Morice it's been a stressful few days. 

"It's hard because you don't sleep, every half an hour you're looking out the window [thinking], 'Where's the red glow at night?'" 

"You're just living on the edge the whole time." 

The mercury rose to a record-breaking 49.5 degrees Celsius at Ceduna on South Australia's far west coast yesterday.

District Council of Ceduna Mayor Ken Maynard said the extreme temperatures "could be a sign of the things to come".

"Yesterday, you only had to walk outside and it [the heat] was instantly wrapped around you; you could really feel it," Cr Maynard said.

"Any bare skin was just burning; it was really radical.

"I went for a drive late in the afternoon to see what people were doing and virtually had the street to myself. There was literally no-one around, unsurprisingly.

"I guess we have to learn to live with it … the main thing is we keep the power on."

A new Emergency Warning has been issued to some towns surrounding the Carlisle River fire in the Otways.

Residents in Barongarook, Gellibrand, Kawarren and Lovat have been told to evacuate immediately.

The warning covers the area closest to the fire in the map below: 

The warning says the fire may impact the towns about midday.

"If you are located in these areas, it is recommended you evacuate immediately and move to a safer location away from the fire," the warning says.

For more specific information about the warnings, visit the VicEmergency website.

Asthma Australia has warned that bushfire smoke can create a danger for people with the condition, even at low levels.

"Fine particles inflame the airways and make it difficult to breathe," CEO Kate Miranda said.

"People with asthma should minimise smoke exposure, follow their Asthma Action Plan, take their reliever or anti-inflammatory inhaler as prescribed, and watch their symptoms closely.

"If symptoms do not improve or worsen, seek medical care immediately. In an emergency, call Triple Zero (000)."

She said people should avoid going outdoors when the air quality was poor, and stay inside with doors and windows closed, using an air purifier if possible. 

You can check the air quality forecast for Victoria, where bushfires are currently burning, at the EPA's website. Today, "good to poor" air quality is expected in the state's south-west region.