South-east Queensland's rapidly filling Wivenhoe Dam began releasing floodwaters on Friday night as downpours continue across the catchment region.
The massive rain band that has drenched the region in recent days has seen the dam's water level jump.
Wivenhoe has risen to 100.2 per cent of capacity, with rain still falling and more inflows expected.
At the start of the week the dam was at 56 per cent of capacity.
Wivenhoe Dam released water at a low rate at 10pm yesterday before it was stopped at 11pm due to downstream flooding.
The flooding was not as a result of releases from Wivenhoe Dam.
Moderate flooding is likely along the Brisbane River downstream of Wivenhoe Dam.
In Ipswich, west of Brisbane, widespread moderate to major flooding is occurring along the Bremer River and Warrill Creek.
Seqwater has urged people to stay away from fast-flowing or deep water downstream.
The Bureau of Meteorology (BOM) has a major flood warning in place for the Upper Brisbane River.
"Significant river level rises are occurring in parts of the upper Brisbane River in response to continued heavy rainfall," the BOM said in its warning on Saturday morning.
"Additional areas of heavy rainfall are forecast for Saturday, which may lead to further river level rises across the upper Brisbane River catchment."
Wivenhoe Dam was built in the 1980s to provide flood protection to south-east Queensland after the devastating 1974 floods.
In 2011, releases from the dam contributed to extensive flooding in Brisbane and Ipswich.
Brisbane's other two major water storage sites, Somerset Dam and North Pine Dam, are also releasing water to cope with the significant rain event.
Somerset Dam began releasing water on Wednesday night.
The suburbs of Joyner, Lawton and Petrie are likely to be affected around rivers and creeks.
Water is also being released from Enoggera Dam in Brisbane, which is at 197 per cent — meaning it is at the limit of its flood mitigation capacity.
Flood alerts remain current for a number of communities in the Gympie, North Burnett and Darling Downs regions.
The Defence Force is stepping in to help.
Defence Minister Peter Dutton tweeted that two helicopters from Amberley air base will assist with evacuations from flood-affected areas.
Queensland Fire and Emergency Services commissioner Greg Leach described the weather event as one of the most severe the south-east has seen in a decade.
"This is an incredibly serious and potentially a life-threatening situation that's unfolding and it's escalating quickly in terms of flash flooding and rapidly rising catchments," he said.
David Grant from the BOM said conditions were expected to last into Saturday afternoon.
"With many catchments saturated, there is a high risk of dangerous and life-threatening flash flooding," he said.
"We are expecting this event to continue into at least Saturday morning, with conditions to last potentially into the afternoon to the evening, with hopefully it to clear by Sunday."
