A heatwave blamed for raging bushfires and a spate of deaths has eased a little in Australia's densely populated southeast, but a ban on lighting fires in the open remained in force.

Temperatures slipped below 40 degrees Celsius in most major centres for the first time in several days, but parts of Melbourne and Adelaide still recorded temperatures above that mark.

Although the bushfires had subsided somewhat, Prime Minister Kevin Rudd warned Australians against complacency, describing the southern part of the country as a ‘tinder box’.

Authorities fear several elderly people may have died due to the heatwave, after 22 ‘sudden deaths’ were reported in Adelaide yesterday.

In Melbourne, power was largely restored after blackouts left hundreds of thousands of homes in the dark, but a major bushfire was still burning in the east of Victoria state.

A spokesman for the state's Country Fire Authority said the fire had destroyed 15 homes, consumed 6,000 hectares and was just two kilometres away from a major power line.

However, fires elsewhere in the state had largely been brought under control.

Authorities believe some of the fires were started deliberately and have maintained daily 'fire bans' for most areas, under which it is illegal to start a fire.