The Brisbane River banks have been evacuated near the CBD after a crane on a pontoon broke free of its moorings near the Story Bridge on Monday afternoon.

Police are concerned the crane could smash into the Howard Smith Wharves or damage the Story or Gateway Bridges, with a tugboat en route to try to secure it.

Emergency services are monitoring the pontoon carrying the crane which is tilting but largely stationary, with evacuation notices for the wharves and riverside walkways downstream still current late on Monday afternoon.

"It's associated with the construction of the green bridge there and has become partially compromised," Queensland Police Deputy Commissioner Steve Gollschewski told Seven Network.

Meanwhile, a man found dead in his submerged car with his his dog in the Currumbin Valley on the Gold Coast became the eighth person to die in the southeast's floods.

There are also "grave concerns" for two men missing in floodwaters in inner Brisbane and at Glen Esk

Major flooding is underway on the Brisbane, Logan, Bremer and Mary rivers, and Warrill Creek ahead of another high tide on Monday night.

"We didn't know that was going to happen, this is Mother Nature,"" Premier Annastacia Palaszczuk said.

"I can't control Mother Nature, the people of this state can't control Mother Nature, and sometimes they throw stuff at us and we've got to deal with it."

Emergency services have made almost 600 swift-water rescues and responded to more than 9000 calls since the rain began last Tuesday.

The Brisbane River peaked at 3.85m on Monday, below the 2011 flood peak of 4.46m, but it's set to rise again to 3.7m at 9am on Tuesday.

More than 15,000 homes are set to be impacted in Brisbane and 3600 in Gympie, north of the Sunshine Coast, with 1544 people in evacuation centres.

Epidemiologist Hilary Bambrick is looking after two neighbours whose home is flooded, while water has also damaged her own Red Hill residence.

"Water came pouring through the wall. It was like someone had turned on a hose," she told AAP.

The Logan-Albert river has also broken its banks leaving hundreds of homes isolated and it's expected to start inundating homes on Monday night.

At Maryborough, north of Gympie, which was flooded last month, residents were bracing for flooding above the 2013 peak of 10.7m.

"Everyone's pretty much reluctantly settling into the fact that we're going to go through it again. There's not much we can do about it," Doug Cuzens, from the Maryborough Services Memorial Bowls club, told AAP.

More than 54,000 homes are without power, but drinking water supplies are secure with the main Mount Crosby Water Treatment Plant back online after flood debris clogged its filters on the weekend.

Schools have been closed and public transport has been mostly suspended across the southeast, while dozens of roads and major highways have been cut by floodwaters, but the Bruce Highway north of Brisbane has reopened.

Bureau of Meteorology forecaster Diana Eden said 70cm of rain had fallen in many areas in the past week, with Mount Glorious topping out at 1.5m.

"Some of the rainfall totals that we've seen over the course of this event have been approaching rainfall totals that we would normally expect over the course of a year," she said.

There have also been reports of looting in the Ipswich suburb of Goodna, where Councillor Paul Tully said up to 150 homes were facing inundation.

Prime Minister Scott Morrison said disaster assistance payments would be available for affected communities and the Defence Force would be deployed to help clean up.

The weather bureau said there could be more severe thunderstorm activity in the region from Wednesday, with damaging winds, hail and heavy rainfall.

However, it would not be as intense as the last week.

Australian Associated Press