Adelaide hit a sweltering 46.6 degrees Celsius on Thursday afternoon, creating a new temperature record and becoming Australia's hottest city in the process.

Adelaide's previous high of 46.1C was set in 1939. That record was beaten by quite some distance and those overall records go back 130 years.

As the temperature continued to climb, it went on to surpass the previous state capital city record of 46.4C set in Melbourne in 2009.

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Temperatures also reached 40s across the border in Victoria, but it was somewhat cooler in Melbourne where the mercury reached 38C. It is expected to be 44C on Friday.

With the heat comes the inevitable concerns about bushfires. Warnings are in force across much of the country, as is often the case at this time of the year.

There are 27 fires burning in Tasmania and 66 across Victoria. The most dangerous conditions are expected to peak on Friday.

Total fire bans are in force across both states as temperatures continues to rise and gusty winds approach 100km an hour across the southeast of the country.

There will be a brief respite from the heat as the weekend begins when a cold front is expected to pass through, swinging the winds round to a cooler southwesterly direction.

The temperature in Adelaide is forecast to reach 31C on Friday and remain in the high 20s this weekend.

Melbourne can expect a high of 27C by Saturday and 23C on Sunday. That should come as some relief for the tennis players and their fans at the finals of the Australian Open.