Once-in-a-century flooding in part of the eastern Australian state of Queensland looks set to worsen as the nation's weather bureau on Saturday warned of more heavy rain in the area.

Some residents have already been evacuated after days of monsoon rains lashed the region around the coastal city of Townsville, in the north of the state, a spokesman for the Bureau of Meteorology said.

Adam Blazak, a forecaster with the bureau, did not say how many people had been evacuated, but added that some areas had reached "major" flood levels.