Residents are being urged to move to higher ground as major flooding is due to hit Brisbane.
The Brisbane River has broken its banks and the Australian Weather Bureau says the biggest floods to hit Brisbane since the mid-1970s will arrive within 48 hours.
The Brisbane River is predicted to reach 4.5 metres on Wednesday and by Thursday.
It is expected to rise above the 1974 peak of 5.45 metres, when 14 people died and 6000 homes were flooded.
Queensland Premier Anna Bligh said "Ipswich and Brisbane are now facing their greatest threat and their toughest test in more than 35 years".
"Now is not a time for panic, now is the time for us to stick together. We are facing one of our toughest ever tests, we will only pass this test if we are calm", she said.
The Brisbane City Council predicts 6500 homes and businesses across 80 suburbs will be inundated over the next few days and about 16,000 properties will be partially affected by floodwaters.
Some areas have received up to 150mm of rain in three hours reports the ABC.
Large parts of Brisbane were already affected by flooding on Tuesday afternoon with a number of shops in the CBD evacuated.
The police urged residents in the inner riverside suburb of West End, and two suburbs north of the city centre to move to higher ground as water entered low-lying streets.
And residents in more than 30 other suburbs are being warned to prepare for flooding.
At Ipswich, the Bremer River is expected to peak at 22 metres - 1.5 metres above the 1974 level.
Ms Bligh says up to 3000 people are expected overnight at the biggest of the four evacuation centres set up, at the Ipswich Showgrounds.
Caboolture, north of Brisbane, is now isolated by floodwaters and some residents are being forced to flee their homes, with nothing more than they can carry because the water is rising so fast.
Much of the rain that fell in the Toowoomba region, causing devastating flash floods, is making its way into the Brisbane River.
The water is expected to move into the catchment of the Wivenhoe Dam system that feeds Brisbane.
The Wivenhoe Dam, which was built in the wake of the 1974 floods, is pumping record amounts of water over its spillway.
On Tuesday, the dam was already at 173% and levels were rising, its maximum capacity is 225%.
The Brisbane City Council says more than 200 homes and businesses along the river are at risk, most at Rocklea, Albion, Milton and Auchenflower.
