More than 3,000 people in towns across the State of Victoria were forced to leave their homes as floods rose to record levels, submerging 13,000 properties.
In Melbourne 8,000 homes lost power as high winds and rain squalls struck the city.
In Tasmania roads and bridges were severely damaged by flash floods and 500 people were evacuated as unseasonal heavy rains struck the north of the island.
Several towns in northern New South Wales are still cut off by high waters leaving 6,000 people stranded.
In the Queensland capital Brisbane thousands of volunteers turned out for a second day helping residents whose homes were hit by the flood clean up mud and debris left by receding floodwaters.
But inland the search continued for 15 people still missing since flash floods roared through towns upriver from Brisbane last Monday and Tuesday. Sixteen bodies have been found so far.
The floods came after four weeks of heavy rains in the entire eastern half of the
Climatologists warn wet weather will continue in the region for several more months due
to a stronger-than-normal effect of the warm Pacific Ocean current known as La Nina.
Australian Bureau of Meteorology climatologist Agata Imielska said La Nina could last until March and global warming may be playing a role in keeping La Nina stronger and lasting longer.
"In 2010, we had record warmest sea surface temperatures and that has implications upon weather," Imielska told the Australian Broadcasting Corporation.
Professor Neville Nicholls of Monash University in Melbourne said there was still not enough research to prove the floods and warm oceans were linked to global warming.