Temperatures cooled from record highs across much of southern Australia on Wednesday, reducing the danger from scores of wildfires that have blazed for days.

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

The Bureau of Meteorology will calculate later Wednesday whether Tuesday's average was even hotter. With Wednesday's cool-down, the national capital, Canberra, dropped from a high of 36 C on Tuesday to 28C and Sydney dropped from 43C to 23 C.

No deaths have been reported, although around 100 people haven't been unaccounted for since last week when a fire destroyed around 90 homes in the Tasmanian town of Dunalley, east of the state capital of Hobart. On Wednesday, police spokeswoman Lisa Stingel said it's likely most of those people simply haven't checked in with officials.

"There are no reports of missing persons in circumstances that cause us to have grave fears for their safety at this time," Tasmania Police Acting Commissioner Scott Tilyard said in a statement.

Thousands of cattle and sheep as well as wildlife are suspected to have been killed.

In Victoria state, north of Tasmania, a fire injured six people, destroyed four homes and caused the evacuation of the farming community of Carngham, Country Fire Authority operations officer Ian Morley said.

Cooler conditions on Wednesday had brought relief to firefighters who would work through the day to build earth breaks to fully contain the fire ahead of warmer temperatures forecast for Friday, Morley said.

"We have had very mild, cool conditions overnight which is a great help to the fire suppression effort," he said.

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

Fires have burnt through more than 131,000 hectares of forest and farmland since Tuesday, but the Rural Fire Service has reported only one home destroyed there.

A fire was burning out of control in the Kybeyan Valley east of the town of Cooma.

Police knocked on doors to advise residents of the danger, with the blaze predicted to move toward the villages of Dangelong, Numeralla and Countegany.

Rural Fire Service Deputy Commissioner Rob Rogers said the cool reprieve was expected to be short-lived, with temperatures forecast to climb again by the end of the week.

"We don't need new fires today," he said.

The fires have been most devastating in Tasmania where at least 128 homes have been destroyed since Friday.

Hundreds of people remain at two evacuation centres in the state's south, as fires continue to burn more than 80,000 hectares since last week.

"People have lost everything. We can't comprehend that devastation unless we are in their shoes," Tasmanian Premier Lara Giddings said.

The fires have consumed over 80,000 hectares in Tasmania since last week.

Wildfires are common during the Australian summer. Fires in February 2009 killed 173 people and destroyed more than 2,000 homes in Victoria state.