Hundreds of thousands of people in Australia's Queensland state were without power on Sunday after Alfred, a downgraded tropical cyclone, brought damaging winds and heavy rains, sparking flood warnings.

Significant damage and power outages are possible in the densely populated region of Queensland, where tropical cyclones impacts are not uncommon but direct landfalls are.

Authorities turn their focus to the threat of flooding and flash floods as communities in south-east Queensland and northern NSW are warned the risks "can't be trivialised".