Earlier, police said the dead included a woman and a boy, whose bodies were found in the Toowoomba CBD.
A man and a boy were also dead after being washed away in, or from a house, at the valley community of Murphy's Creek.
Heavy rain across the whole of southeast Queensland today will worsen the flood disaster and hamper search and rescue efforts for dozens of people missing or stranded.
The weather bureau says heavy rain will continue across the whole of southeast Queensland today, and this could lead to more flash flooding.
The rain will last for most of the day, a Bureau of Meteorology forecaster told AAP.
"We expect the system to weaken late today or tomorrow," he said.
A severe weather warning was issued early this morning, saying heavy falls may lead to localised flash flooding and/or worsen existing river flooding.
Heavy rain and thunderstorms are expected to continue through the Southeast Coast, Darling Downs and Granite Belt, the far southern parts of the Wide Bay and Burnett and eastern parts of the Maranoa and Warrego districts.
Road closures will also hamper rescue and recovery efforts.
The Warrego Highway, the main east-west road across the Darling Downs is closed in several places. On the Toowoomba Range, north of Toowoomba, police say it will be closed indefinitely.
At the Gatton bypass, the highway will be closed until at least 4pm NZT on Tuesday.
Motorists have been urged not to travel to Queensland's southeast corner unless absolutely necessary.
Queensland's Main Roads Minister Craig Wallace has pleaded with motorists to avoid all non-essential travel around Toowoomba, Lockyer and Ipswich.
Lockyer Valley Mayor Steve Jones said everything possible was being done to help people caught up in the disaster, which has sparked mass evacuations across the valley.
"We've got an evacuation centre at the Gatton shire hall, it's almost full at the moment," he told the ABC.
"We've got people at the community hall at Heildon and we've also got them at the state school at Withcott.
"And we've got people at Grantham actually still here on higher ground near the school."
- AAP