Ms Gillard said the 12-month tax, starting from 1 July, would be levied on those earning A$50,000 or more, and those affected by floods would not pay.

"We should not put off to tomorrow what we are able to do today," she said.

More than 30 people have been killed since flooding began last month.

"The Treasury's preliminary estimates are that GDP growth in this financial year will be about half a percentage point less due to the floods," Ms Gillard said.

"The best preliminary estimate of the direct cost to the federal budget of the summer's flood disaster is A$5.6bn."

As well as the tax, cuts to government spending will help meet the reconstruction bill.