Southeast Queensland residents are facing very dangerous thunderstorm activity and potentially life-threatening flash floods as a deadly low-pressure trough pummels the region.
Residents in Gympie, north of the Sunshine Coast, are preparing for major flooding amid warnings the Mary River could reach levels not seen since major flooding in the area in February 1999.
The river peaked at just under 22 metres during that event 23 years ago, and the Bureau of Meteorology is warning of heavy rainfall over the next 24 hours.
The catchment area has already recorded falls in excess of 300 millimetres over the past day.
Meanwhile, flood sirens have sounded in Grantham, in the Lockyer Valley Region west of Brisbane, with residents in low-lying areas told to move to higher ground.
Two people have already died in floods triggered by the weather system - with a 54-year-old man killed trying to ride a motorbike through rising water at Gympie and a 63-year-old woman found dead in a submerged car on the Sunshine Coast.
There are currently no people reported missing but drivers are still failing to heed warnings, Emergency Services Deputy Commissioner Mark Roche said.
"We are actually seeing the footage of people driving into floodwaters, actually making a decision to drive into floodwaters," he said on Friday.
"That puts their lives at risk, puts their passengers at risk, and also all the emergency services that are required to go out there and conduct those rescues."
A number of people were found clinging to trees in rescues on Friday morning, with swift-water teams responding to almost 40 incidents since Wednesday afternoon.
"People should not be on the roads in events like this, we knew this event was coming," Mr Roche said.
The Bureau of Meteorology has issued a "very dangerous thunderstorm" alert for residents in the Gympie, Somerset, Sunshine Coast and Noosa areas for Friday.
The forecaster warns intense rain from the slow-moving weather system could put people living in Kenilworth, Eumundi, Mapleton, Yandina, Conondale, Nambour and the area west of Conondale at risk.
"Intense rainfall that may lead to dangerous and life-threatening flash flooding is likely," the BoM said in its alert.
Emergency services are expecting some properties in the Gympie area to be inundated and are keeping an eye on the Mary River, Queensland Police Deputy Commissioner Steve Gollschewski said.
While the BoM predictions are helpful, emergency services "don't know what's actually going to happen" until the rain falls, he said.
Friday morning's briefing predicted the weather event would begin to ease on Friday night and into Saturday.
The Department of Transport said flash flooding had cut dozens of roads in Brisbane, Bundaberg, the Darling Downs, the Gold Coast Hinterland, Gympie, Ipswich, Moreton Bay, Noosa, the Sunshine Coast and its Hinterland, and Toowoomba.
A large trough has been battering the state's southeast - mostly areas north of Brisbane - causing flash floods and moderate flooding for almost four days.
The BoM said an area north of Biggenden recorded 423mm of rain in the 24 hours to 5am on Friday, with 389mm falling in just four hours.
