Sydney sweltered through one of its hottest days on record Sunday as temperatures soared in southern Australia and authorities imposed a fire ban in a sizzling start to summer.

Australia's largest city recorded its hottest day since 1939 as the mercury rose to 47.3 degree Celsius (117.14 degrees Fahrenheit) in the western suburb of Penrith.

More than 200 weather records were broken nationwide during the last summer, with intense heatwaves, bushfires and flooding plaguing the December 2016-February 2017 season.

Top tennis players were called off the courts Sunday at the Sydney International, a warm-up tournament for the Australian Open Grand Slam, after thermometers recorded temperatures over 40 degrees Celsius.

The heat took its toll on French star Kristina Mladenovic, who retired midway through her match citing heat stress.

"43degrees but probably 50 on court when started. I'm sorry to the fans. I think it's 1st time in my career I retired a match..it says it all," the world number 11 tweeted.

Australian and English cricketers slogging through the final Ashes match in Sydney may have also experienced the hottest day on record for a Test match in Australia.

The hottest Test day on record appeared to be 43.1 degree Celsius in Adelaide in 1908, the Bureau of Meteorology told the Sydney Morning Herald.

Weather stations near the Sydney Cricket Ground were recording maximum temperatures of 43.4-43.7 degree Celsius Sunday.

Total fire bans were imposed to reduce the risk of bush fires, which are common during Australia's arid summers.

Numerous blazes had already sprung up on Saturday, with several homes and buildings lost in bush fires in the states of Victoria and South Australia.

Australia has warmed by approximately 1.0 Celsius since 1910, according to a report from the weather and national science body CSIRO.

Experts have also warned that climate change had pushed up land and sea temperatures, leading to more extremely hot days and severe fire seasons.