Authorities are assessing whether to evacuate buildings in Bundaberg in southern Queensland after a marine supplies business was washed away on the bank of the Burnett River overnight.
Ten businesses on Quay Street, including a multi-level hotel, may be deemed unstable after last month's record flood.
A 20-metre section of the Burnett River bank has collapsed from the rain and a section of the Midtown Marina Store in Quay Street has 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."
Mayor Mal Forman says much of the area along the river is fragile.
"The way it's happened is very frightening to see it collapse so quickly and such a large area, but I think when you look down there's areas that could fall away as well," he said.
Nick Heenan manages a multi-storey hotel and says he is concerned he may have to evacuate the building.
"We are keeping a very close eye on it and also through last night - that's when we noticed the building had proceeded into the sinkhole," he said.
"It's only half of it - the upper lower level of the building has gone into it."
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."
© ABC 2013
12:00 EDT Heavy rains have damaged homes and flooded roads in Western Australia's Mid West region.