A 20-metre section of the Burnett River bank has collapsed from the overnight rain, washing away part of a building in Bundaberg in southern Queensland.

A section of the Midtown Marina Store has been washed away.

Owner Jan Douglas says it happened about 7:30am (AEST).

"I came into work early, went down and took some photographs and it was already dropped into the water, but it was held up by a farm gate onto the front of the roller door for safety," she said.

"You could hear the creaking and we saw it slowly just topple into the sinkhole."

Meanwhile, the weather bureau says the low pressure system that caused yesterday's heavy rain in the Wide Bay is now moving south.

Falls of more than 100 millimetres were recorded since 9:00am yesterday at Rainbow Beach and Lady Elliot Island.

There is still a flood warning for the Mary River, with falls of 150 millimetres recorded in the catchment.

Bureau spokesman David Grant says there will be patches of rain today, but nothing like yesterday.

"We are expecting it to become fairly slow-moving today while deepening a bit further, continuing to rain at times," he said.

"We may hear the odd crack of thunder but really generally just scattered showers tending to rain at times."