More than 30 homes are feared destroyed by bushfire in the state of South Australia, with officials warning that lives are in danger even as weather conditions improve.

The warning came on Sunday as firefighters continued to battle an out-of-control blaze which broke out on Friday in the Mount Lofty Ranges east of Adelaide.

The state's Country Fire Service said the intense fire was continuing to burn in all directions, threatening lives.

But a cool change on Sunday is expected to help them work to contain the fire ahead of a forecast rise in temperatures again on Wednesday.

"I can confirm that 12 homes have been destroyed and it's feared that a further 20 homes have also been lost," Jay Weatherill, the South Australian prime minister, told reporters.

"However, the conditions for firefighting have improved. The weather is cooler and the weather conditions will permit aerial firefighting."

Weakening winds

More than 11,000 hectares have been burnt in the Adelaide Hills, an area in the Mount Lofty Ranges with a population of about 40,000. It is dotted with scenic villages and known for its farming produce and wineries.

Temperatures are forecast to soar to 39 degrees Celsius on Wednesday, but the winds are not expected to be as strong as they have been over the past two days, said Greg Nettleton, the Country Fire Service chief executive.

Hundreds of firefighters from the neighbouring states of Victoria and New South Wales were joining their South Australian counterparts on Sunday, taking the total number of crew battling the blaze to more than 800, the AFP news agency reported.

About 22 people, mostly firefighters, have suffered minor injuries from the fire, Weatherill added.

State officials said on Saturday it was the worst fire conditions they had seen since the 1983 bushfires of Ash Wednesday.

The 1983 disaster killed more than 70 people in South Australia and Victoria and destroyed thousands of homes and buildings.

In Victoria, cooler temperatures on Sunday saw bushfire warnings downgraded across the state. But thousands of sheep and other stock were believed to have been lost in separate blazes there, officials said.

Bushfires are common in Australia's summer months between December and February. Often started by lightning, the fires spread rapidly in the usually tinder-dry bush; woodland or forest usually containing gum trees.

The gum tree, otherwise known as the eucalyptus, is ubiquitous in Australia and produces antiseptic oil which is explosively flammable. 

"Black Saturday", the worst firestorm in recent years, devastated southern Victoria in 2009 as it razed thousands of homes and killed 173 people.

Source: Agencies