SYDNEY (AP, AFP, REUTERS) - Australia experienced its hottest day on record and temperatures are expected to soar even higher as heatwave conditions hit most of the country.

The Australian Bureau of Meteorology said the average temperature across the country of 40.9 deg C on Tuesday beat the record of 40.3 deg C from Jan 7, 2013.

"This hot air mass is so extensive, the preliminary figures show that yesterday was the hottest day on record in Australia, beating out the previous record from 2013 and this heat will only intensify," bureau meteorologist Diana Eadie said in a video statement on Wednesday.

The weather bureau said temperatures in southern and central Australia on Thursday may reach between 8 and 16 deg C higher than normal.

On Wednesday, temperatures soared to 47.7 deg C in Birdsville, Queensland, 46.9 deg C in Mandora, Western Australia and similar levels in southern and central Australia.

The highest temperature reliably recorded in any location in Australia was 50.7 deg C in January 1960, at Oodnadatta, a desert settlement in outback South Australia.

The town of about 200 people on an old Aboriginal trading route is forecast to record peak temperatures of 47 deg C on Wednesday, according to the Bureau of Meteorology, making it one of the hottest places on Earth.

High temperatures and strong winds are also fanning bushfires around Australia, including more than 100 in New South Wales state where heat and smoke have caused an increase in hospital admissions.

"Over the next few days we are going to see firefighters, the emergency services and all those communities close to fires...challenged with a new threat," New South Wales fire commissioner Shane Fitzsimmons said on Wednesday.

New South Wales Premier Gladys Berejinklian warned: "We are going to have a number of fronts that are gong to fuel, or escalate the fires burning, but also the potential to have spot fires and embers travelling very long distances."

Australia is being hit with two separate climate-driving events off its west and southern coasts - a positive Indian Ocean Dipole and negative Southern Annulare Mode - that are reducing rainfall and increasing temperatures.

"They have combined together to create this situation of a particularly nasty heatwave event," said meteorologist Sarah Scully at the Bureau of Meteorology.

The extreme conditions have been exacerbated by a warming climate, which is triggering large-scale protests in a country that is committed to exploiting its vast coal reserves.

The combination of thick smoke settling over populated areas and intense heat has triggered numerous health warnings, especially for the young and the old, and those with respiratory conditions.

"People should take those conditions seriously and do what they can to keep out of the heat as much as possible," said Mr Richard Broome, the director of environmental health in New South Wales state.

Cooler conditions are forecast from Friday.