Australia experienced its third-hottest year on record in 2014, paving the way for an early start to the bushfire season, scientists said Tuesday as hundreds of firefighters battled blazes in three states.

The biggest concern is a huge blaze in South Australia's Adelaide Hills, with firefighters racing to contain the inferno which has already destroyed up to 38 homes ahead of worsening weather conditions.

Wildfires are also burning in Western Australia and the southern state of Victoria, officials said, as the Bureau of Meteorology confirmed 2014 was "Australia's third-warmest year since national temperature observations commenced in 1910".

"Much of Australia experienced temperatures very much above average in 2014, with mean temperatures 0.91 degrees Celsius above the long-term average," said the bureau's Neil Plummer.

The weather agency said that following Australia's warmest year on record in 2013, both maximum and minimum temperatures remained well above average in 2014, with "frequent periods of abnormally warm weather".

The years since 2002 have seen seven of Australia's 10 warmest years on record, it added.

Sarah Perkins, a research fellow at the University of New South Wales' Climate Change Research Centre, said Australia had sweltered through prolonged and extreme heatwaves in 2014 and its hottest spring on record.

"These warm conditions, particularly in spring, contributed to yet another early start to our bushfire season, and recent heatwave events have also contributed to heightened bushfire risk and poor firefighting conditions currently in South Australia," she said.

"The fact that we are experiencing such record-breaking and extreme conditions, both during consecutive years and since the turn of the millennium, is a clear sign that climate change is happening now, and here, in Australia."

Higher temperatures are not the only cause of bushfires, she said, with rainfall and winds among the other factors.

"But certainly when it's hotter, things dry out more quickly, particularly if we have a very intense heatwave... which increases the risk of intense bushfire weather," she told AFP.

Will Steffen from the Climate Council said it was no surprise that 2014 was the third hottest year behind 2013 and 2005.

"The impact of climate change on these trends is very clear. Climate change is making Australia hotter and more prone to bushfires," he said.

The Adelaide Hills bushfire, in scrubland of Sampson Flat northeast of the city, has left 167 buildings damaged or destroyed since Friday, including up to 38 homes, officials revealed Tuesday.

In the worst-affected town of Kersbrook, 12 homes were lost or badly damaged.

In total 23 people were hospitalised due to the blaze, but all but two had since been released. One man is in a serious condition after he was injured by a falling tree.

The state's Country Fire Service has warned higher temperatures and windier conditions are expected on Wednesday.

University of Melbourne climate scientist David Karoly said the high temperatures across Australia in 2014 indicated a need to address the amount of greenhouse gas pollution blamed for climate change.

"Unless there are rapid, substantial and sustained reductions of greenhouse gas emissions in Australia and globally, Australia will experience more heatwaves and bushfires as in 2014," he said.