Brisbane residents are bracing themselves for a huge flood surge flowing from the Toowoomba region, which is expected to peak on Thursday.
Officials say between 6,500 and 9,000 homes and businesses could be inundated in Queensland’s capital city.
Thousands of residents have already fled parts of the city which faces a combined surge of water from the flooded Lockyer Valley and the overflowing Wivenhoe Dam.
Authorities have warned that the Brisbane River which cuts through the city will rise above the 5.45m (17.9ft) peak reached during the 1974 flood.
The river’s banks have already reportedly been breached in some places and lower lying suburbs have already been flooded.
Mayor Campbell Newman said: “Today is very significant, tomorrow is bad, and Thursday is going to be devastating for the residents and businesses affected.”
State Premier Anna Bligh urged people to prepare themselves: “We need to make every effort to stay calm and stick together. If you live on high ground, now is the time to reach out and offer help to neighbours… and offer a bed for the night.”
“I think the entire city of Brisbane, the Ipswich region and most of the south-east, needs to prepare ourselves for enormous disruption.”
Flash floods have already devastated southern Queensland leaving 10 people dead and more than 70 people missing and has caused billions of dollars worth of damage.