The death toll has risen to four after an SES volunteer was killed en route to a rescue near Ipswich overnight and a 54-year-old man's body was found in floodwaters at Stones Corner in inner east Brisbane on Saturday.
Queensland Fire and Emergency Service Commissioner Greg Leach says the SES volunteer died after the car they were in was swept away, but three other volunteers made it to safety.
"We pass on our condolences to family friends and loved ones," he told reporters on Saturday.
"We'll continue to support the family as best we can in coming days and weeks."
There are also searches underway for two people missing, one at Gympie, and one at Yadina on the Sunshine Coast.
Emergency services have made 132 flood rescues and responded to more than 2000 call for help in the last 23 hours.
The southeast is awash on Saturday as rain buckets down from a huge low pressure trough, which has been sitting over the region for five days.
More than 70cm of rain fell at Mount Glorious in the 21 hours to 6.30am on Saturday, the Bureau of Meteorology said, with rainfall exceeding half a metre in many other places.
"In some parts of southeast Queensland, this is the biggest event that they will see in a number of decades and the rain has not stopped, Police Minister Mark Ryan said.
"In fact, there are some parts where it is intensifying."
The BoM warned of "dangerous and life-threatening" flash floods from Hervey Bay to Yarraman, Toowoomba and Ipswich on Saturday, and further south to the NSW border on Sunday.
"It's extremely dangerous out there in southeast Queensland at the moment," Mr Leach said.
"Catchments are completely saturated, our rivers are rising, we have flash flooding, now is not the time to be out and about."
Gympie is set for its worst floods in 23 years on Saturday when the Mary River level rises above the 21.95m level it reached in the city 1999.
Downstream at Maryborough, the river is on Sunday set to rise higher than 9.95m reached during major floods in that city just last month.
Residents along the Maroochy River, and at Tewantin on the Noosa River, are set for their biggest floods in 30 years on Saturday, while major flooding is also forecast for Palmview on the Moloolah River.
Woodford and Gregor Creek are also set for flooding above the 2011 levels after releases from Wivenhoe Dam into the Upper Brisbane River.
Ipswich is preparing for its worst flooding in a decade on Sunday with the Bremer River to rise above a 2013 peak of 13.9m.
Minor flooding is forecast along the Brisbane River at Moggill and Jindalee on Saturday, and even in the Brisbane CBD with a high tide on Sunday.
There were 253 people in evacuation centres in Moreton Bay, Sunshine Coast, Ipswich, Maryborough and Gympie on Saturday morning.
Dozens of roads are cut, including the Bruce Hwy at multiple locations between Brisbane and Maryborough and the Warrego Hwy between Brisbane and Toowoomba.
Ferry services have also been halted indefinitely due to dangerous debris in the Brisbane River.
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