Heavy precipitation in the northeast part of the country has led to rising waters around Cairns, a popular tourist destination that serves as a gateway to the Great Barrier Reef.
The city has been almost completely cut off by floodwaters, and local officials fear its 160,000 residents will soon lose access to clean drinking water.
Cairns received about 600mm (23.6 inches) of rain over 40 hours from Saturday through early Monday morning, more than three times the December average.
All flights into and out of Cairns Airport were cancelled or postponed on Monday. Some planes were even partially submerged by the flooding.
In addition, more than 14,000 properties across the region are without power, according to authorities.
But the threat from the extreme weather extended well beyond Cairns. In Wujal Wujal, a rural community in the Cape York region, nine people, including a seven-year-old boy, sought shelter overnight on the roof of a hospital, as floodwaters mounted around them.
They were only able to escape on Monday morning. Authorities in the area have weighed an aerial evacuation of Wujal Wujal, but the continued rainfall has stymied efforts.
The flooding follows heavy rains and strong winds brought on by former Tropical Cyclone Jasper, which made landfall in Australia last week.
Queensland state Premier Steven Miles said the scale of the storm was unprecedented. “We see a lot of natural disasters, and this is just about the worst I can remember.”