Australia was home to all 15 of the world's hottest temperatures on Tuesday, a feat it may well repeat on Wednesday and beyond as a huge swath of the nation bakes in 45-degree-plus heat.

A slew of records have already fallen during the current heatwave and more are likely to be broken before a cool change breaks up the furnace later this week.

Most of inland south-eastern Australia is expected to reach 45 degrees or warmer on Wednesday. Bureau of Meteorology

According to the El Dorado Weather site, the warmest 15 places on the planet in the past 24 hours were all in Australia. These ranged from Tarcoola in inland South Australia, which reached 49.1 degrees, to Yulara in the Northern Territory at 46.1 degrees in 15th slot.

The Bureau of Meteorology said the 49.1 degrees at Tarcoola was a record reading for that site.

Australia often dominates heat temperatures in summer, given that rival southern hemisphere sites are mostly in South America and South Africa where readings above 40 degrees are not so common.

The Bureau of Meteorology with an update on the severe heat conditions over southern and central Australia and also a forecast for the rest of the week.

The world's hottest places in the 24 hours to 11am (AEDT) on January 16:

Tarcoola (Australia) 49.1°C Port Augusta Aws (Australia) 49°C Woomera Aerodrome (Australia) 48°C Olympic Dam Aerodrome (Australia) 47.9°C Hay Airport Aws (Australia) 47.8°C Oodnadatta Airport (Australia) 47.7°C Marree Aero (Australia) 47.6°C Coober Pedy Aws (Australia) 47.5°C Warburton Airfield (Australia) 47.3°C Ivanhoe Aerodrome Aws (Australia) 46.9°C Wilcannia Aerodrome Aws (Australia) 46.6°C Leigh Creek Airport (Australia) 46.3°C Wulungurru (Australia) 46.2°C Moomba Airport (Australia) 46.1°C Yulara Aws (Australia) 46.1°C

50 degrees?

Jacob Cronje, a senior meteorologist with Weatherzone, said he "wouldn't be shocked" by a 50-degree reading during the current spell, given the scale and intensity of the heat.

"Certainly the duration of this event and the spatial extent of the heatwave across the southern half of Australia seems to be quite significant," he said.

"By the end of the week, we should see many records broken across NSW," Mr Cronje said, adding that northern Victoria might have to rewrite the records too.

Australia has posted only three days above 50 degrees using standardised equipment, the most recent being in February 1998 when Mardie in Western Australia reached 50.5 degrees. The other two occurred in January 1960 when Oodnadatta Airport in South Australia reached 50.7 and 50.3 on consecutive days, the bureau said.

Wildlife like this goanna near Menindee on the Darling - and all other life forms - are being roasted in extreme temperatures across inland Australia. Dean Sewell

Much of the NSW Riverina and most of Victoria's north can expect 45 to 47 degrees on Wednesday, with little relief in daytime maximums until Friday or Saturday.

By 1.45pm Wednesday AEDT, all the mainland states had reached 40 degrees, White Cliffs in western NSW hit 48.2 degrees, Victoria's Swan Hill reached 45.9 degrees and Tarcoola was anything but cool at 48.4 degrees.

According to the bureau, January 12-15 have already made it into the list of top 10 warmest days on record for Australia for area-averaged maximum and mean temperatures.

Humid times

Both Melbourne and Sydney cities will be spared the worst of the heat, but inland suburbs will be a lot warmer.

Even so, high humidity, particularly in Sydney, would make for some very uncomfortable nights, particularly Friday into Saturday, Mr Cronje said.

Coastal Sydney suburbs will most likely feel several degrees warmer due to high humidity. Dominic Lorrimer

Minimum temperatures for Saturday morning of about 24 degrees for coastal Sydney suburbs will most likely feel several degrees warmer.

For Canberra, temperatures may reach 40 degrees for four days in a row, a series not recorded before for the nation's capital. No days of 40 degrees were recorded in Canberra between 1973 and 1998, the bureau said. The city reached 41.6 degrees on Wednesday.

South-eastern Australia with see most unusually warm conditions on Wednesday. BoM

Health warnings

Health authorities in several states have issued warnings for people to take care of themselves, their relatives, neighbours and their pets as heatwave impacts can build over several days.

An added threat in Sydney will be the high ozone air pollution expected across the city in coming days.

Richard Broome, director of environmental health at NSW Health, said "ozone can irritate the lungs, and people with asthma need to follow their Asthma Action Plan and have their relieving medication with them".

"Ozone levels are higher outdoors than indoors, and generally highest in the afternoon and early evening, so limiting time outdoors during the heat of the day and in the evening helps people to not only keep cool but to limit their exposure to ozone pollution," Dr Broome said in a statement.

Those most at risk were residents with asthma and other respiratory diseases such as chronic obstructive pulmonary disease, and anyone experiencing severe respiratory distress should seek immediate medical help, the statement said.

The coming cool change will shift a blocking high in the Tasman Sea, which has helped inland temperatures build up in recent weeks.

Another band of heat will follow by early next week, lifting temperatures in Sydney's west back towards the high 30s, although the warmth is unlikely to match that of the current heatwave, Mr Cronje said.

Hot years

The Bureau of Meteorology and the CSIRO's State of the Climate report identified rising temperatures as among the clearest indications of climate change in Australia.

Globally, last year was the world's fourth-hottest year, according to the Japan Meteorological Agency. All of the five warmest years on record have happened since 2014, the agency reported this week.

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