Concern the most devastating effects of Cyclone Alfred may come in its wake

The slow-moving storm is expected to reach the southern Queensland and northern New South Wales coast tonight or early tomorrow morning.

Heavy rainfall and damaging wind gusts are already developing along the coast, with daily rainfall totals of up to 400 millimetres possible.

ABC Correspondent Digby Werthmuller says extreme flooding is expected in the days following the cyclone.

He says the Australian Defence Force has handed out more than 300-thousand sand bags and several planes and flood rescue teams on standby.