A weekend of intense heat in Western Australia has seen 36 locations, including Perth, record their warmest November day on record and now the hot air mass is on its way to the eastern states.

Perth was among a group of cities and towns to post record temperatures for November as it sweltered through 40.4 degrees Celsius on Saturday.

Meanwhile the Mid West town of Morawa hit 45C and further inland, Dalwallinu topped out at 43.5C.

By Sunday the blistering conditions had set new records for towns in the east of WA, with Kalgoorlie Airport reaching a scorching 44.7C and Esperance Airport hitting 42.2C.

The Bureau of Meteorology (BOM) said the heat was generated by a slow-moving trough which pulled exceptionally hot air from northern and central parts of WA to the south.

"A trough was located near the west coast on Saturday and that dragged some unprecedented hot temperatures from northern parts of the state down over the south-west including the metro area [resulting in] record November temperatures," BOM forecaster Steph Bond said.

"The trough moved inland on Saturday night which caused that hot air to move into the Goldfields and south-eastern parts of the state."

The cool waters at Lucky Bay at Esperance, off Western Australia's south coast, would have been extremely inviting on the weekend. ( ABC Open contributor cozzas_photography )

While a milder change swept over the south-west of the state on Sunday, the heat has lingered over the south-east.

But by mid-week a cold front will bring relief to the southern half of WA, which will see temperatures drop into the low 20s as the hot air is pushed interstate.

"On Wednesday we expect a cold front to move through the southern parts of WA bringing a cooler air flow and this will push all the hot air into South Australia … which will then travel in to New South Wales," Ms Bond said.

Heatwave building in the east

South Australia is bracing for record-breaking temperatures and strong winds on Wednesday, with catastrophic fire conditions expected in the state's central districts.

The Country Fire Service has taken the unusual step of declaring a pre-emptive fire ban across South Australia on Tuesday, ahead of the catastrophic conditions expected on Wednesday.

Temperatures across most of the state are expected to soar above 40C, including in Adelaide where 42C is forecast, along with gusty winds and areas of dust haze.

From mid-week into the weekend, a large part of inland New South Wales and Southern Queensland will be in the grip of a low-to-severe intensity heatwave, elevating the fire danger in areas that have already been affected by bushfires.

The NSW Rural Fire Service has confirmed 476 homes have been destroyed in NSW since the start of the bushfire season and more than 1.6 million hectares have been burnt.

Firefighters are working to build containment lines ahead of the deteriorating weather conditions this week.