Residents in North Queensland are being urged to prepare for the worst storm to hit the state since Cyclone Yasi in 2011.
Tides are expected to peak at 3.2 metres, with a storm surge expected at three to four metres above that.
It would present a threat to low-lying areas like parts of Mackay, almost a thousand kilometres north of Brisbane, and Bowen.
Up to 25,000 people in low-lying areas of Mackay were urged to evacuate.
Queensland Police Commissioner Ian Stewart has described the evacuation as one of the biggest operations ever undertaken.
"We've certainly moved whole towns before, but nothing of this magnitude. We've moved virtually whole suburbs as well, but, again, this is right across Mackay, because of the unique landscape and the low-lying areas."
Commissioner Stewart has also called on those who live in safer areas of Mackay to help their neighbours.
"We'd ask other people who live in safer areas of Mackay to open their hearts and their homes to their friends. Certainly, there's the opportunity, if you're not in any of the affected zones, to put your hand up, call a friend and say, 'Listen, bring your family to my place.' You know, hopefully, it will just be for a night."
Queensland premier Annastascia Palaszczuk says people must cooperate with the authorities.
"We are very concerned at the moment about the prospective tidal surge in Mackay. Many people know, living in Mackay, it is quite low-lying."
Meanwhile, Greens M-P Adam Bandt is being criticised for linking Cyclone Debbie to coal-fired power.
Mr Bandt says Prime Minister Malcolm Turnbull will be partially the cause of deaths from events like Cyclone Debbie if he invests government funds in fossil fuels.
"If Malcolm Turnbull uses scarce public money to build a new coal-fired power station, he'll have blood on his hands, because, the more coal we burn, the more extreme weather events like Cyclone Debbie or Cyclone Yasi we'll see, and people will suffer."
Opposition Leader Bill Shorten says Mr Bandt is doing the people of North Queensland a disservice with those comments.
