A cool change is not expected to sweep across Australia for days as large parts of the country prepare for more sweltering heatwave conditions.

Heatwave conditions are set to persist for large swathes of the country with a cool change not expected until later in the week.

Severe to locally extreme heatwave conditions are extending through northern parts of SA, much of southwest Queensland and into northern and eastern NSW.

A wave of hot air had some regions swelter through temperatures that peaked in their mid-40s on Tuesday.

The Bureau of Meteorology is forecasting both maximum and minimum temperatures in the heatwave-affected areas to be 5C to 10C above average throughout the rest of the week.

Senior bureau meteorologist Dean Narramore said that was unlikely to lead to record-breaking highs, but temperatures in some areas were likely to be similar to those experienced during the 2019-20 Black Summer bushfire season.

“A lot of those areas saw temperatures around 48-49C at the time, whereas those inland areas are now looking at probably 47-48C,” he said.

Low-severe intensity #heatwaves continue across much of the country. Locally extreme heatwaves are impacting Pilbara/Gascoyne.

Extreme Fire Dangers for parts of the Pilbara coast today and tomorrow.

A cool change will develop from Wednesday.

More: https://t.co/jlOoTZL1iF pic.twitter.com/6mNUQ8NFk1

— Bureau of Meteorology, Australia (@BOM_au) January 23, 2024

The NSW Rural Fire Service said it expects to see elevated fire conditions towards the end of the week.

Temperatures in NSW are set to reach the mid-30s to low-40s during the day in many centres when the mercury reaches its highest on Thursday and Friday.

Severe heatwave conditions will develop across the central and northern inland parts of the state, spreading east towards Sydney, the Hunter and mid-north coast on Wednesday and Thursday.

“We could even get back to back 39C at Newcastle which is a little bit unusual there and even Maitland getting into the low 40s,” Mr Narramore said.

Regional centres including Armidale, Moree, Nowra, Orange and Wollongong are all set to bear the brunt of the heat.

Some regions in the northwest slopes and plains, such as Walgett, are expected to reach 42C on Wednesday, while parts of upper-western NSW, including Wilcannia, could peak at 46C.

At the Little Topar Roadhouse, about 80km northeast of the NSW outback town of Broken Hill, owners Jo Lindsay and Kim Starkey were getting ready to bathe their 17-month-old macaw Charlie Girl in the stifling heat.

The pair were largely without customers due to a lack of people stopping for a bite as the temperature soared towards the mid-40s.

One trucker sat out front next to the petrol pump about midday, keeping out of the heat in the comfort of his air-conditioned cab.

“We’re just keeping cool and entertaining ourselves with birds,” Mr Starkey told AAP.

“(Charlie) just started saying ‘goodnight’. Last night was the first time.”

Severe heatwave conditions are also forecast for SA’s northwest, northeast and Flinders regions, with some areas expected to hit the mid-40s.

It will be another scorching day for the southern state after its capital nudged 41C on Tuesday afternoon, the first day over-40C of the year.

Mr Narramore said the very hot air from inland areas – some of which could experience temperatures as high as 48C during the week – would reach eastern parts of NSW by Friday.

“Thankfully a cool change will move into southeastern parts of the country by Friday then sweep through NSW on Friday night and Saturday, dropping temperatures back to average or even slightly below for the weekend,” he said.

Emergency services have urged people to watch out for signs of heat stroke or heat exhaustion.

Extreme fire dangers are also forecast for parts of the Pilbara coast on Wednesday.