There will be extreme heatwave conditions in south-west Queensland and north-west New South Wales over the next three days, the Bureau of Meteorology (BOM) says, with several outback towns expecting sweltering daytime temperatures of at least 43 degrees Celsius.

BOM senior forecaster Jonty Hall said it was potentially "dangerous" weather.

"We expect at the lower levels of heatwave it may become a threat to the less healthy — like the old and infirm or very young — but even healthy adults may experience some problems once you get up into the extreme [heatwave] range," he said.

The heatwave is forecast to persist for several days, with Birdsville in Queensland's far south-west expecting tops of 45C, Thargomindah 44C, Windorah 43C and Quilpie 43C.

Mr Hall said it was more than just the usual heat that western Queenslanders expected during the summer months and nightfall would bring no relief from the oppressive conditions.

"We're talking between 5 and 8 degrees above average, both in the day and overnight, so it's the prolonged nature of that heat that can really cause problems through there," Mr Hall said.

Map shows red areas of extreme heatwave situation for 3 days from December 17, 2017. ( Supplied: Bureau of Meteorology )

Birdsville pub ready for summer sizzle

The manager of the iconic Birdsville hotel, Ben Fullagar, said he was ready for an influx of hot, thirsty locals.

"We just spend time making sure all of our refrigeration equipment is running the way it should be and obviously, more importantly, we make sure all the beers are nice and cold," he said.

Mr Fullagar said western Queenslanders were "resilient" when it came to the heat, but electricity bills were set to soar.

"Pretty much once this heat starts this week we don't really turn our air-conditioners off until March or April, because basically if you turn them off, it's too hard for them to cool the place down again the following day," Mr Fullagar said.

BOM said Wednesday could bring some relief, with a south-westerly wind change bringing cooler air up from southern Australia, pushing the heat into eastern Queensland to parts of the Darling Downs.