Greg Ansley: Brisbane watches disaster loom

Pathways are flooded as the river bursts its banks. Photo / Getty Images

The heart of Brisbane was in a torpid, surreal calm late yesterday as water from the Brisbane River poured into its outer suburbs and Ipswich to its west fought for survival.

As dark, muddy waters pumped debris at incredible speed through a downtown area becoming isolated and eerily quiet after power was cut to businesses and offices, hundreds of people lined the river's banks to watch the approach of disaster.

"It's extraordinary, just awesome," said 28-year-old Craig Hubert. "This is something you'll see only once in 100 years."

The waves that raged down the slopes of the Toowoomba Range and across the Lockyer Valley after Monday's lethal flash floods were taking another heavy toll as Brisbane braced for its worst peak, expected to hit at 4am (7am NZT) today.

The death toll rose to 12 yesterday with the discovery of two more bodies, adding to the 12 killed by earlier flooding in the state.

As many as 43 people were still missing last night, so the toll is expected to increase as teams using military helicopters scour the devastated Lockyer Valley for more victims.

"It's a heartbreaking task they're facing," Premier Anna Bligh said.

Yesterday, Ipswich joined the list of cities and towns drowned by Queensland's worst floods in a century.

Water submerged the central city and 3000 homes, forcing mass evacuations, before surging on towards Brisbane.

From the air early in the afternoon, floodwaters could be seen creeping through dozens of homes on Brisbane's fringes.

By late afternoon, 35 suburbs were under water, and officials said up to 20,000 homes were likely to be affected.

Power has also been cut to 70,000 homes and businesses in southeast Queensland.

By early evening, hundreds of Brisbane residents had fled to evacuation centres, joining the more than 3500 evacuated in other areas.

Thousands more are isolated by floodwaters in northern NSW.

In Brisbane's centre, the power and height of the river water has snapped boats from their moorings, ripped away parts of houses, snapped trees, pulled out water tanks and driven a mass of debris towards the ocean.

Bystanders reported watching the pontoons of the Oxley on the River restaurant, its tables and umbrellas intact, floating down the river.

Army demolition experts were also late yesterday deciding whether to blow up two vessels - the party boat The Island and the Moggill Ferry - which had been torn from their moorings and were threatening to carve a destructive path downstream.

Darry Gaffy, who lives in the suburb of Indooroopilly about 7km upstream of Brisbane's central business district, said the river's surge was "well and truly" more powerful that its flow during the disastrous 1974 floods.

His wife, Elizabeth, who was carried to safety as a 6-year-old when her home was lost to those floods, agreed, saying: "It was not anywhere as fast as this."

The river is expected to peak at 5.5m this morning, just above the 1974 level.