Authorities say the flood threat facing Brisbane and Ipswich is worse than the 1974 disaster.

Heavy rain, releases from Wivenhoe Dam and high tides will be a damaging combination.

The Brisbane City Council predicts 6,500 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.

Meanwhile, the death toll from yesterday's flash flood in the Lockyer Valley, west of Brisbane, has risen to nine.

Ms Bligh says the Brisbane River will continue to rise into Thursday.

"Ipswich and Brisbane are now facing their greatest test and toughest threat in 35 years," she said.

"We will only pass this test if we are calm, if we are patient with each other ... and if we listen carefully to the instructions we are being given.

"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."

The Brisbane River is predicted to reach 3 metres tonight, 4.5 metres tomorrow, and by Thursday it is expected to rise above the 1974 peak of 5.45 metres.

The Bremer River at Ipswich is now expected to reach 22 metres tomorrow morning - 1.5 metres above the 1974 level.

Ms Bligh says the situation in Brisbane and Ipswich is continuing to deteriorate.

"We are now in a very frightening experience," she said.

Large parts of Brisbane are already affected by flooding. A number of shops in the CBD have been evacuated and the State Library has closed because of the extreme weather conditions.

A steady stream of debris is floating down the swollen Brisbane River, including boats ripped from their moorings by the force of the current, and a whole ferry pontoon.

A floating riverside cafe in Milton is under threat from the swollen river.

Building contractor Barry Howland says a walkway is bolted down, stopping the cafe from floating away.

"Unfortunately it's tied on with a steel point here that we need to cut to free it," he said.

"Water has come in so fast, it's over the pumps, we can't pump out the hole, so we need an emergency pump so we can pump that out.

"But other than that, if we could just get that cut away, she'll float, she won't sink, but now the water's coming over the top, I don't know."

The nearby Regatta Hotel is being sandbagged.

No 'shock absorber'

Brisbane Lord Mayor Campbell Newman says the situation is changing rapidly.

"If it keeps raining all night and tomorrow the way that it's been raining in the catchment today, well who knows what happens then on Friday," he said.

"Wivenhoe has protected Brisbane over the last few weeks from flooding. Unfortunately the big shock absorber that is that dam is now full."

Prime Minister Julia Gillard will fly to Brisbane tonight as the flood crisis worsens.

She has told Channel Seven the situation is very grim and it will take many months for communities to recover.

"We're going to be working with them through the Defence Force also through making available emergency payments," she said.

Lawyer Tony Conaghan says his Waterfront Place office was evacuated this morning.

"I was here for the '74 flood, so I just hope that it's going to not be as bad as that," he said.

"As long as we get some rain stopping, hopefully, and a bit of recess in it, it might be OK. It's not looking good at the moment."

An evacuation centre is being set up at the RNA Showgrounds in Bowen Hills, which can accommodate 3,000 people.

A council spokesman says residents must bring bedding, any medication, important documents and spare clothes, but no pets are allowed at this point.

And in Ipswich, the showgrounds has been declared the evacuation centre.

Several roads across the region are cut including major highways, while roads that are not already under water are choked with people trying to get home.

West End evacuation

Police say residents in the inner-city suburb West End should move to higher ground as the water enters low-lying areas.

Police have been stationed on roads leading to Riverside Drive to prevent all but local traffic from accessing the area.

A large section of the drive is under water after the river broke its bank earlier today.

Further north at Strathpine, residents and businesses are evacuating as the Pine River swells, and Caboolture is completely isolated by floodwaters.

Residents close to the Brisbane River and associated tributaries including the Bremer River, Six Mile Creek, Bundamba Creek and all other tributaries are being told to monitor the situation overnight and take evacuation measures if required.

The flood crisis has also forced the Royal Brisbane and Caboolture Hospitals to cancel all elective surgery.

Defence Minister Stephen Smith says the ADF is sending more helicopters to south-east Queensland to help with the flood rescue effort.

"Two additional Black Hawk helicopters will be assigned and based at Amberley for the present, and four light helicopters - observation helicopters - particularly well suited for observation and search and rescue will also be deployed to Amberley," he said.

A spokesman says all emergency procedures will continue and the wards are fully staffed.

A telephone hotline - 1300 993 191 - has been set up for people seeking information on friends and relatives caught up in the flooding disaster.