Australian police and defence forces have searched burned-out vehicles and homes in the towns worst hit by wildfires on the island of Tasmania, where more than 40 fires still raged.

The blazes began on Thursday on the state's thinly populated southeastern coast, amid a fierce heatwave and strong winds.

The heat eased over the weekend, slowing the fires, but late today firefighters issued an emergency warning for residents in Taranna, 47km east of the state capital Hobart, where a fire burning for more than three days threatened residents.

The national weather bureau warned that this weekend's relative mildness would be a brief reprieve, with extremely hot conditions set to return to much of the country early next week.

The fires that continue to burn in Tasmania have cut off communities and hampered efforts to search devastated areas.

In the small town of Dunalley, 56km east of Hobart, more than 65 homes and a school have been destroyed. Nearby Boomer Bay and Marion Bay have also suffered damage.

Acting Police Commissioner Scott Tilyard told the Australian Broadcasting Corporation there were about 100 people with whom authorities are still trying to make contact.

It may take days to determine whether the fires have killed anyone during what is the peak holiday season on the island.

"We're hoping very much along with everyone else that there won't be (any deaths), but we need to go through the process to confirm that there haven't been," Mr Tilyard told the ABC.

Tasmania experienced its peak temperature since records began at 41.8C on Friday, when much of mainland Australia sweltered in similar conditions and fires burned across several states.

The heatwave, which began in Western Australia on 27 December and lasted eight days, was the worst in more than 80 years in that state and has spread east across the nation, making it the widest-ranging heatwave in more than a decade, according to the Australian Bureau of Meteorology.

Fire crews from Victoria and South Australia headed to Tasmania to help fatigued crews there, while fires burned on in mainland states South Australia, Victoria, and New South Wales.

Bushfires are a major risk in the Australian summer, which brings extreme heat, dryness, and strong winds.

Authorities warned earlier in the summer that much of the country faced extreme fire conditions this season.

The "Black Saturday" fires, the worst in Australia's history, killed 173 people in Victoria in February 2009.

Australia's wheat harvest is unlikely to be affected by the fires and hot weather, as the vast majority of this season's crop has been harvested, analysts said.