Firefighters across Australia continued to battle blazes overnight, taking advantage of cooler conditions before extreme highs hit again tomorrow.

Record temperatures across southern Australia cooled yesterday, reducing the danger from scores of raging wildfires.

However, it is expected to bring only a brief reprieve from the summer's extreme heat and fire risk.

Australia had its hottest day on record on Monday, with a nationwide average of 40.33C, narrowly breaking a 1972 record of 40.17C.

In Tasmania, a blaze that destroyed more than 100 homes in the southeast is still out of control, the Australian Broadcasting Corporation reported.

A cool change brought relief to firefighters in Tasmania and gave them the chance to build earth breaks to try to contain the blazes.

"Crews at all the incidents across the state should get a good opportunity to start really consolidating some of the containment lines they've already constructed today," said Mike Brown, Tasmania’s Chief Fire Officer.

Commissioner Shane Fitzsimmons from New South Wales Rural Fire Service warned about further dangers as the mercury rises this weekend.

"We're looking at temperatures across much of New South Wales in to the low/mid 40s tomorrow and certainly extending into the high 40s on Saturday," he said.

In New South Wales, Australia's most populous state, firefighters were battling 141 fires, including 31 that had not yet been contained.

Fires burning out of control near the towns of Cooma, Yass and Shoalhaven were the most concerning.

A fire was burning out of control in the Kybeyan Valley, east of Cooma, local media said.

In the state of Victoria, a fire injured six people, destroyed nine homes and caused the evacuation of the farming community of Carngham west of the city of Ballarat, the Country Fire Authority said.

Residents there voiced anger today that they were not given enough warning before the fires hit, local media reported.

Alan Goodwin, Victoria Fire Chief, warned residents not to get complacent.

"Crews have worked hard overnight to consolidate containment lines around ahead of the severe fire weather that we're expecting tomorrow," he stated.

In Queensland, on Bribie Island, a large fire that was burning out of control has now been contained.