The Ipswich City Council, west of Brisbane, has downgraded its expected flood peak of 19 metres.

The Bremer River is now likely to peak tonight at 17.2 metres.

That is two metres lower than during the disastrous 1974 floods.

As many as 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.

Kalbar evacuated

Low-lying parts of Kalbar, south-west of Brisbane, are being evacuated.

Mayor John Brent says there has been seven hours of continuous rain this morning.

He says Warrill Creek is rising rapidly and homes flooded in 1974 have been evacuated.

"We're concerned ... for the safety of people," he said.

"[We want to] ensure they are in their home if its safe and others have gone to friends or relatives or moved into a central location here in Kalbar.

"We're also looking at the Boonah position as well, in regards to the rising waters in the Teviot."