Flooding in the south-west Queensland town of Charleville has been declared a disaster situation as hundreds of homes face inundation.
Two-thirds of properties are likely to go underwater by the end of Tuesday as heavy rains swell a local creek and river.
About 500 people will be evacuated following the emergency removal of 45 elderly people from a nursing home.
Emergency Services Minister Neil Roberts made the disaster declaration this afternoon.
"The declaration gives Emergency Services agencies the power of mandatory evacuations if required," Mr Roberts said.
"Bradley’s Gully which runs through the centre of Charleville was recently at 3.1 metres and rising to 3.5 metres.
"During the 2008 Charleville floods the Gully peaked at 3.2m, illustrating the significance of this flood event."
The town's levee is expected to remain in tact, however.
Residents have already begun moving to higher ground and a woman and child had to be rescued from their car after it was swept off the road by floodwaters.
Queensland's south-west has been pounded by a large monsoonal trough that has dumped the best rainfall in almost a century over the southern outback.
Along the coast, the effects of the weather system are also being felt, with two days of solid rain falling over Brisbane, the Gold and Sunshine coasts.
Up to 94 millimetres has been recorded on Brisbane's northern bayside in just the past 24 hours, while Nambour, on the Sunshine Coast, received 150 millimetres in the same period. Weather forecasters have warned the region could record up to 200 millimetres by 9am Wednesday.
A low pressure system forming over Fraser Island is also expected to complicate matters, bringing buffeting winds of up to 100kmh by this afternoon.
About 6000 customers were left without power in parts of Brisbane, the Lockyer Valley and Gold Coast hinterland this morning as a result of weather-related network problems.
The Bureau of Meteorology has issued a severe weather warning including possible flash flooding and damaging winds across the region, while at least one Sunshine Coast school cancelled classes as a safety precaution.
Fallen trees and a landslide over the road at Mount Glorious also beset morning commuters and emergency workers.
State Emergency Service workers have been sandbagging at Noosa, while 40 people in Brisbane logged emergency calls for help overnight, mostly involving leaking roofs.
The rain is expected to continue throughout the day, easing to showers later this afternoon as the trough pushes north and out to sea. Weather forecasters say it could be next week before clear skies return over the south-east corner.
The RSPCA has warned property owners to move livestock to higher ground amid the risk of mass drownings and animals being caught in mud.
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