Temperature records have been broken in towns across parts of Australia sweltering through a heatwave, which is currently in its fourth day.

Australia also recorded its hottest December on record the Bureau of Meteorology said on Thursday in a special climate statement on “the unusual extended period of heatwaves” across much of the country.

December 27 was the hottest on record for nationally averaged mean maximum temperature (40.19C) and the second hottest day on record for any month.

Nine places in New South Wales broke temperature records on Wednesday – including six all-time records, according to the Bureau of Meteorology.

Whitecliff, in the state’s north-west, recorded the highest maximum temperature in NSW of 48.2C just before 3.30pm – an all-time high for the area.

Far-western towns of Wilcannia, Menindee and Ivanhoe are all tipped to reach 48C on Thursday, as the high-intensity heatwave continues.

The NSW-Victoria border cities of Albury and Wodonga reached their hottest day on record, at 45.3C.

Quick Guide Heatwaves and climate change in Australia Show According to the Bureau of Meteorology and the CSIRO, Australia has warmed by 1C since 1910, and temperatures will increase in the future. So how will climate change affect future heatwaves in Australia? The CSIRO and BoM have compiled different models for predicting the outcome of climate change in Australia to produce a guide to how different regions will likely be affected. They found that every part of Australia will continue to experience increases in average temperature, and will have a higher frequency of hot days.

The duration of hot spells will increase in every region. In many areas in the northern half of Australia, the average number of days above 35C could increase by two to three times.

Late in the century, towns such as Darwin, Alice Springs and Broome may experience days with temperatures above 35C for about a third of the year. These higher temperatures will also result in higher evaporation, which will continue to make drought conditions worse.

The Bureau of Meteorology on Thursday confirmed the statistics for the past 24 hours, warning there was more hot weather on the way.

“The extreme heatwave across northern Victoria produced a few records yesterday: 45.3C in Albury-Wodonga was its hottest day on record, that record spanning over 30 years,” senior meteorologist Rod Dickson said.

Other centres posted in the record books, with Mangalore, two hours north of Melbourne, reaching 44.8C, its hottest January day on record. And the northern township of Yarrawonga’s maximum of 45.7C was its equal hottest day.

“Broadly speaking across the north yesterday temperatures ranged between 45 and 46 degrees, so some pretty extreme heat,” Dickson said.

Overnight brought only slight relief, as temperatures dipped to about 27C.

Over the past three days, maximum temperatures across South Australia have been running 10 to 14 degrees above average.

In its climate statement for the past month, the Bom also said Christmas Day had been Australia’s warmest Christmas since records began, and Boxing Day was also the warmest on record.

“Australia’s overall mean temperature for December was the highest on record, 2.13C above the 1961–1990 average and more than 0.3C warmer than the previous record from 1972,” the Bom said.

“Record high State and Territory averaged mean temperatures were also seen in New South Wales, Victoria, Tasmania, and the Northern Territory; Western Australia and South Australia were second-warmest, and Queensland was third-warmest.”

The climate statement said Australia’s mean maximum and mean minimum temperatures for December were also record warm, with the mean minimum more than half a degree above the previous record from 1972.

Numerous states this week have enacted health warnings related to the heatwave, which is ongoing.

Sujata Allan is a member of Doctors for the Environment and works as a GP in Blacktown, where temperatures regularly exceed those in the CBD.

She has spent six years working on and off in western Sydney, which can have maximum temperatures that are as much as 10C higher than in coastal areas, and sees the impact a changing climate can have on human health.

“Western Sydney has a lot of people who are more at risk. Western Sydney has some of the most economically disadvantaged people in the country and higher rates of chronic illness.”

Allan said she had treated one patient for heat stress this week who worked in a factory that wasn’t well-ventilated, and she regularly sees elderly patients who struggle in the heat if they don’t drive and have poor public transport connections.

Some regional centres posted record highs on Tuesday, including Port Augusta and Tarcoola where the mercury climbed close to 50C.

Tarcoola was among the hottest spots again on Wednesday with a top of 48.7C while Coober Pedy had 47.8C and Woomera 47.6C.

SA’s State Emergency Service is maintaining an extreme heatwave emergency warning and the state government has declared a code red during the current conditions.

Total fire bans are in place across much of central NSW, stretching from the Victorian border up to Queensland.

Temperatures in Sydney’s west are expected to climb as high as 45C by Friday, ahead of an expected cool change on Saturday.

Authorities are again warning people to take extra care in the heat by staying indoors, keeping hydrated and limiting physical activity during the extreme heat.