Australia experienced its hottest month on record in January, despite floods and storms that devastated parts of the country's east, officials said.

The Bureau of Meteorology said both the average mean temperature of 29.68 degrees Celsius (85.42 degrees Fahrenheit) and the average mean maximum temperature of 36.92 Celsius surpassed previous records set in January 1932.

The nation's central outback sweltered under a "dome" of heat for much of the month, with the Northern Territory posting its hottest mean temperature on record for January of 31.93 Celsius, the bureau said.

"The heatwave in the first half of January was exceptional in its extent and duration," it said in a statement released Friday.

"The national average maximum temperature on 7 January was the highest on record. Numerous stations set records for the most days in succession above 40 degrees Celsius, including Alice Springs (17 days) and Birdsville (31 days)."

The bureau said a large number of weather stations set all-time record high temperatures during the heatwave, including Sydney (45.8 Celsius on January 18) and Hobart (41.8 Celsius on January 4).

The highest temperature recorded during the heatwave was at Moomba in South Australia, which hit a scorching 49.6 Celsius on 12 January.

The bureau said the heatwave, which aided bushfires in the eastern states, was followed by extreme rainfall and flooding for some coastal areas of Queensland and New South Wales caused by ex-tropical cyclone Oswald.

The rain caused extensive flooding in the Queensland towns of Bundaberg, where some houses were washed away and roads destroyed, and Gladstone among others.

"Gladstone received 820 millimetres (32 inches) of rainfall in four days, which exceeded its previous record for a whole month, and more than the annual rainfall recorded in 2011 or 2012," the bureau said.