yclone Debbie, a category four storm, has left at least 45,000 homes without power and damaged buildings, although it is too early to say how many.
PM Malcolm Turnbull told parliament he had activated a disaster response plan.
More than 25,000 people were urged to evacuate their homes ahead of predictions the cyclone would be Queensland's most damaging since 2011.
The system is expected to remain for several hours after crossing the coast between Bowen and Airlie Beach.
"We are in for a long, tough day," said Queensland Premier Annastacia Palaszczuk.
"The intensity and ferocity of the winds is going to be gradually increasing. Everyone is bunkered down."
Cyclone Debbie could be the most powerful storm to hit the area since Cyclone Yasi in 2011
Electricity providers said it was not known when power would be restored to houses.
"We're getting reports of roofs starting to lift, even in some of our own facilities in the Whitsundays," said Queensland Police Deputy Commissioner Steve Gollschewski.
One person in the region compared the winds to "freight trains coming through left and right".
"The trees are going wild. The place is just shaking continuously," the man, identified only as Charlie, told the Australian Broadcasting Corp.
Test of endurance
Forecasters had twice delayed predictions of when the cyclone would make landfall.
Ms Palaszczuk described the storm as "a monster" and compared it to Cyclone Yasi, which had devastated towns and flooded evacuation centres.
She said Monday's emergency evacuation order was "probably the largest ever" for the north-eastern state.
In other key developments:
- Forecasters said the tidal surge would now be less than 2m (6ft), and no longer coincide with high tide
- However, authorities warned there would still be flooding in low-lying areas
- The region is expected to be hit with 150-500mm of rain on Tuesday
- Police warned people to beware of fallen powerlines, which could be deadly
- Emergency stockpiles of food and fuel have been set aside, and the army is on standby
- Insurance Council of Australia, an industry body, declared the cyclone a "catastrophe".
Ms Palaszczuk said that shelters had been made available on higher ground for those with nowhere else to go.
Storm clouds gather in the town of Ayr, 775 miles (1,248km) north of Brisbane, Queensland
More than 2,000 emergency workers are also on standby, but people have been warned crews will only respond when it is safe to do so.
Some residents refused to leave despite warnings that Cyclone Debbie's destructive core could be as wide as 62 miles (100km).
Queensland authorities have closed 181 schools and 232 early childhood education centres.
All flights have been cancelled at Townsville Airport and Mackay Airport.
Police Commissioner Ian Stewart said the weather contributed to the death of a woman in a car crash on Monday.
A satellite image shows Cyclone Debbie
Queensland is preparing for a destructive cyclone