Raging bushfires have destroyed vast forest areas, several homes and a golf club in Australia as emergency crews battled extreme conditions amid some of the hottest temperatures in 100 years.

Tens of thousands of volunteer fire fighters have been deployed across south-eastern Australia to try to contain outbreaks that have destroyed vast areas of forest and farmland as well as a handful of homes.

The giant walls of flame are threatening about a half-dozen towns in South Australia, Victoria and New South Wales as temperatures soared above 45 Celsius.

Six major fire fronts are burning across Victoria. Residents have described smoke so thick it blocked out the rays of the sun as huge walls of fire ripped through wooded areas.

Emergency officials have said that scorching temperatures and strong winds have caused conditions perfect for deadly firestorms. So far, no lives have been lost and authorities have urged residents to stay indoors to escape the stifling heat.

Fires in New South Wales have sent a cloud of acrid smoke over Australia's largest city, Sydney, where crews have fought outbreaks in suburbs close to the city center.

Rob Rogers, the assistant commissioner of the state's Rural Fire Service, says the emergency response requires careful planning.

"It is really a military-style operation," he said. "We have a local incident management team who set up fairly close to the fire scene.  They divide the fire into divisions and sectors and they work out who is responsible for what part of the fire. You have then [an] air operations manager, who will coordinate water bombing operations with what the ground troops are doing."  

Southeastern Australia is one of the world's most fire-prone regions. Hot summer conditions have been exacerbated by a long-standing drought. Backyard barbecues and the use of power tools have been banned in high-risk areas.

A recent report from the Australian Institute of Criminology has revealed that half of all bushfires are deliberately set, while others are started by lightning strikes or accidentally by careless campers or by cigarettes discarded by motorists.

The study shows that about 30,000 fires are started by arsonists each year causing $1 billion worth of damage. The Institute recommends better education campaigns in the community and schools.

Health authorities have reported dozens of sudden deaths that have been blamed on the record heat wave that has gripped the southeastern corner of the Australian continent in recent weeks.

In tropical northern Australia the weather is also creating problems with torrential rain causing major flooding, which has left many communities cut off and homes damaged.