The Brisbane River has broken its banks amid dire predictions of the biggest floods to hit Queensland's capital since 1974.

The weather bureau says the river is expected to reach major flood levels tomorrow afternoon and rise further on Thursday.

It is believed 9,000 homes will be inundated as floodwaters race towards the city.

Some areas have received up to 150 millimetres of rain in three hours.

Water is also rising quickly in the Bremer River at Ipswich, west of Brisbane, where it is expected to peak close to 19 metres.

Police are preparing residents and business owners in the inner-city suburb of West End for the possibility of evacuations later today.

The Brisbane City Council says more than 200 homes and businesses along the river are at risk, most at Rocklea, Albion, Milton and Auchenflower.

Police are advising all residents in low-lying parts of Strathpine and Dayboro to the north of Brisbane to evacuate to higher ground immediately.

Caboolture is isolated so evacuation out of town by car is impossible. Police are saying that people in low-lying areas who can should move to higher ground or prepare for rising water.

The threat to Brisbane comes after an inland tsunami swept through Toowoomba and the Lockyer Valley yesterday, leaving nine people dead and 66 missing.

That wave of brown water is now making its way towards the Brisbane River and catchment areas, where the capital's defence of Wivenhoe Dam is struggling to hold back the deluge.

Officials have had to increase the amount of water being released from Wivenhoe because of major inflows coming from the Lockyer and Brisbane valleys.

The river has broken its banks in parts of West End and water is reportedly slowly creeping onto roads in low-lying areas there.

Buildings in Fortitude Valley and businesses at Eagle Street Pier in the city are also being evacuated.

The potentially looming disaster in the city is being made worse by cut and congested mobile phone lines, making communication difficult. Vodafone customers have been without reception for most of the morning.

People have been asked to stay off telephones unless absolutely necessary to avoid congesting lines for emergency services.

Staying dry

Jodie Craig, who owns the Joynt Hotel on Montague Road in West End, is trying to move belongings to the upper floors of the hotel.

"Up until last night I was freaking out a bit and then this morning I've just been watching the news and I guess I should start doing something," she said.

"I'm going to take all my electrical equipment and stuff that's worth a lot of money upstairs and hopefully it'll be safe up there."

Ms Craig says the ground floor of the hotel was completely submerged in the 1974 floods and she hopes the Wivenhoe Dam is enough to hold back the water this time.

She says she has been without phone reception for several hours and is unsure if police are wanting people to evacuate.

"The road's pretty busy. It's not like there's anyone in uniform telling us to leave," she said.

"I'm really clueless as to what's going on. People are just telling me West End's been told to evacuate. I really don't know. I'll just get my stuff up."

The council in Ipswich has downgraded its expected flood peak of 19 metres.

The Bremer River is now likely to peak tonight at 17.2 metres - two metres lower than during the disastrous 1974 floods.

About 400 streets are expected to be fully or partially under water.

The Ipswich showgrounds has been set up as the town's major evacuation centre. It will also accommodate pets.

No insurance

Being so close to the river means Ms Craig is unable to get flood insurance.

"That's why I wanted to get all the stuff that's the most important to me," she said.

"I mean I'm not going to worry about furniture and things like that, there's not really much I can do."

Police say they have not ordered any evacuations of West End residents or businesses yet but with a high tide expected in just over two hours and a large volume of water still moving down the Brisbane River, that situation could change.

Police have stationed several officers along Riverside Drive between Orleigh Park and the Go Between Bridge at West End.

They are now turning back traffic trying to access Riverside Drive after the decision was made earlier today to close the road.

Translink says bus services have been suspended in the Caboolture, Redcliffe and Burpengary areas because of flooding.

Train services through to the Sunshine Coast are still running.

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