Thousands of homes are without power and buildings have been damaged as a powerful storm has begun to batter Australia's northeast coast.

Cyclone Debbie tore through Queensland causing flooding and bringing down power lines as winds reached more than 160mph at tourist resorts along the world-famous Great Barrier Reef.

The storm made landfall at Airlie Beach, north of Proserpine.

"It's very noisy: Screaming, howling wind ... sounds like a freight train," Jan Clifford told Reuters by text from Airlie Beach as the cyclone hit.

The storm was branded Category 4, the second strongest on the scale of hurricane intensity, but has been downgraded to Category 3.


Image: The areas worst affected by Cyclone Debbie

Thousands of people fled their homes 24 hours before the storm arrived in this biggest evacuation in Australia since Cyclone Tracy devastated the northern city of Darwin on Christmas Day 1974.

A man was seriously injured by a falling wall in Proserpine but no other injuries have been reported so far.

The storm was travelling southwest so slowly that weather forecasters fear the cyclone conditions could last for as long as 24 hours.

Queensland police commissioner Ian Stewart says the public may have to "brace for" the impacts of this "destructive cyclone".

He added: "We are going to get lots of reports of damage, and sadly I think we will also receive reports of injuries, if not death."

Image: Damage at Airlie Beach

Queensland premier Annastacia Palaszczuk says families across Queensland face an "uncertain" few hours.

"This is a slow-moving system and we are seeing families at the moment, they are getting hammered by this system.

"This would be an incredibly scary moment for them."

Prime minister Malcolm Turnbull told parliament that conditions in the region were "deteriorating rapidly".

Mr Turbull said: "The federal and Queensland governments have prepared well for the onset of this cyclone. We have activated the disaster response plan."

Trees have been uprooted with debris tossed into streets and there has been widespread flooding.

Around 38,000 people in the towns of Bowen and Mackay north and south of Airlie Beach are without power.

Ports at Abbot Point, Mackay and Hay Point were shut, Townsville airport was closed and airlines Qantas, Jetstar, Rex and Virgin Australia cancelled several flights to and from the region.

Cyclone Debbie: Footage shows 'monster' storm hit Queensland https://t.co/K3xomGix1p pic.twitter.com/DO0IkHRqyj — Emad Rassmy (@erassmy) March 28, 2017

The cyclone had earlier swept through the Whitsunday islands further east, where tourist resorts were damaged and boats torn from moorings.

Cyclone Debbie is the most powerful storm to hit Queensland since Cyclone Yasi destroyed homes and crops and devastated island resorts in 2011.

A tidal surge was expected to flood low-lying areas near Mackay as the storm whipped up waves and currents and lifted sea levels.