South Australian firefighters work around the clock ahead of high temperatures

Firefighters continue to battle the Adelaide Hills bushfire before a heatwave expected later in the week, with the warning level downgraded to the lowest level.

CFS fireys are hoping to beat back flames in the Adelaide Hills ahead of the incoming heatwave. Source: AAP

A bushfire blackening Adelaide Hills has been downgraded to the lowest warning level as firefighters work around the clock to extinguish the blaze.

An advice warning has been issued on Boxing Day for Cudlee Creek, Castambul, Chain of Ponds, Charleston, Cudlee Creek, Gumeracha, Harrogate, Inglewood, Kenton Valley, Lobethal, Millbrook, Mount Beevor, Mount Torrens, Paracombe, Tungkillo and Woodside.

Exhausted Country Fire Service volunteers catch a short break while battling the Adelaide Hills fire on Friday afternoon. Source: AAP

"At this time there is no threat to life or property and firefighters are attending this fire," a police warning states.

Thermal imaging equipment had been used to identify hotspots, while large trees burnt and flare-ups occurred on the fire ground.

About 25,000 hectares have already been scorched in the blaze.

One person has died, 84 homes have been destroyed and hundreds of other buildings claimed in the fires.

A heatwave bringing severe to extreme conditions will start moving towards the Australian east coast on Thursday, affecting the northern parts of South Australia.

Adelaide will be spared with a top of 33 degrees Celsius forecast before soaring to 39 degrees Celsius on Friday.