Severe thunderstorms hit flood-stricken Southeast Queensland on Wednesday night, dumping more than 100 millimeters of rain in some areas and impeding the recovery effort.
The Queensland floods death toll has reached 20 and is likely to climb with more than 10 people still missing.
Last week, flooding also began to hit the states of New South Wales, Victoria, and even Tasmania.
A 3-year-old boy was found in floodwaters in Central Western NSW on Thursday morning, a day after he went missing.
The floods claimed their first life in Victoria on Wednesday when an 8-year-old boy drowned in the north east of the state.
The Australian government has officially declared the situation to be a disaster in NSW and Victoria to expedite financial assistance to the victims.
Prime Minister Julia Gillard has been visiting affected areas in Queensland and Victoria to assess the damage and give comfort to locals.
With the costs of the crisis rising in each state, Gillard's recent election promises of a budget surplus in 2013 may be challenged.
Earlier this week, Federal Treasurer Wayne Swan said there will be some tough decision-making ahead.
"We do have underlying economic strength to deal with the challenges that are posed by this natural disaster, but of course it will involve difficult decisions for us as we go forward," he said in an interview posted on his website.