Wind gusts up to 100kmh have brought down trees and fences as the cyclone tracks south to south west, with residents from Bowen to Mackay in the firing line as the system crosses the coast, according to the Bureau of Meteorology.
Residents of Marian, about 30km west of Mackay, say roads are closed and water levels are rising after conditions intensified early Sunday morning.
"We are getting absolutely smashed," Stephanie, a mother of one, told AAP.
"Our fence is down, our neighbour's fence is down. The rain is just sideways. There's nothing we can do but just wait it out."
Heavy rainfall has pummelled the town, with the Bureau of Meteorology reporting 146mm of rain in just two hours, just to the west at Gargutt.
"The back yard is flooded - it's worse here than we were expecting."
In Mackay, tourist Josephine Tobias is staying at the Mackay Caravan Park, and says locals know how to cope.
"Honestly, so far here it's not too bad at the moment. We chose to stay, and it's wet, and it's windy, but everything is okay," Ms Tobias said.
"This is the first time I've been through a cyclone, but everyone keeps telling me it's just a category one and not to panic.
"It's like a really bad storm that just keeps going."
Further north in the town of Bowen, residents are on alert as the storm system approaches.
"The wind has just suddenly changed direction," said Karyn, manager of Coral Cove Apartments.
"It's been coming from the south all night, and it's just changed direction in the last 30 minutes," she said.
"It's been raining on and off, and it's pretty gusty, but we will have power."
Heavy rain is hammering Ayr and Mackay, and damaging 100km/h wind gusts have slammed tourism hotspot the Whitsunday Islands.
Overnight falls of up to 200mm were recorded west of Mackay with the bulk of the falls expected in the next two days.
"Cyclone Koji is crossing the coast between Ayr and Bowen," senior forecaster Dean Narramore said on Sunday.
"We can see a lot of rainfall spiralling around the system - it's a very lopsided system with most of the heaviest rainfall near and well south of Tropical Cyclone Koji, and that's why we're particularly concerned about our residents and communities from around the Ayr and Bowen area, down through the Whitsundays."
"That's bringing strong to locally damaging winds and also widespread heavy rainfall that is going to lead to widespread flooding in the coming days, on top of what is already going on through parts of Queensland."
Queensland Premier David Crisafulli praised the preparation of communities that have endured floods in the past.
"I do believe that people have prepared brilliantly for the rain that will come," he said on Sunday.
"If Queenslanders continue to do that then I have every faith we will respond following the event."
Warnings are in place for much of the northeast Queensland coast from Townsville to Mackay, including Bowen, Proserpine and the Whitsunday Islands.
Heavy rainfall leading to flash flooding is developing between Townsville and St Lawrence and tides are likely to be higher than normal between Cardwell and Mackay, the bureau noted.
The heavy downpours could add to already-soaked catchment areas.
After crossing inland on Sunday morning, gales are expected to ease rapidly as Koji weakens and then tracks westwards.
In the northwest, major flooding that has already heavily affected Gulf Country communities - where livestock losses are projected to be significant - continues on the Flinders River.
15°C