Flash floods swept through the tiny town of Clermont, 274km southwest of Mackay, after a deluge of hundreds of millimetres of rain hit the region.
Properties in low-lying areas were inundated and families forced to evacuate to higher ground at the height of the emergency.
After a nervous night, floodwaters started to fall on Tuesday, and residents took stock of the damage.
"I have never seen anything like it in the time I have lived here," Jamie Beale from the local IGA told AAP.
"The floodwaters came up pretty fast.
"The roads are still closed, but there are crews down there at the Sandy Creek bridge clearing it off."
Locals believed it was the worst flooding to hit the town of almost 3000 in decades, he said.
"The people who have lived here for years say the only thing that compares was the flooding in '73, '74. It's definitely the worst I have ever seen."
Three people were rescued after a truck and a second vehicle were stuck in floodwater on the Gregory Highway at 2.40am.
Major flood warnings remain in place for the lower Flinders River and the Georgina, Connors, Isaac and Mackenzie Rivers.
"The good news is, in some places, the floodwaters have been holding, and in areas that have been receding, the weather is starting to clear," Isaac Council Mayor Kelly Vea Vea said.
"However, these things can change. We'll be monitoring it really closely."
Residents are on high alert for ongoing flooding as former Tropical Cyclone Koji continues to weaken as it slowly tracks northwest.
Severe rainfall warnings have now been cancelled, but showers and isolated thunderstorms are forecast.
The small highland community of Eungella, west of Mackay, was expected to be cut off for up to three months.
Aerial footage posted to social media showed the steep mountain road blocked by huge landslips, with the bitumen buckled and large sections having fallen away.
The northwest is on high alert for more flooding as the remnants of Koji move inland.
It is still reeling from a monsoon that impacted the region, devastating livestock and isolating towns.
Close to 50,000 stock are already missing or presumed dead in the Gulf Country.
Premier David Crisafulli thanked local communities for their preparation and resilience in the face of the cyclone.
He said the government was continuing to drop fodder and medical supplies for stricken animals, but warned that losses would increase.
"Those communities are so reliant on those grazing industries, and this is going to be a massive blow.
"There will be individuals who are impacted on a really large scale, and the prospect of more rain in the days and weeks ahead will send a shiver down their spine."
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