Almost 26,000 homes and businesses were swamped by the torrent as the Brisbane River rose 15ft on Wednesday.
The international community has begun to donate funds for the relief efforts, with the Queen understood to have made a private donation yesterday.
State premier Anna Bligh fought back tears to speak of an “unrecognisable” city swamped in flood water.
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She said: “Queensland is reeling from the worst natural disaster in our history. We now face a reconstruction task of post-war proportions.”
She said the river would take several days to subside and warned it may be months before people can return to their homes.
Yet more rain is forecast for the next two days.