Queenslanders woke up on Wednesday to a huge cleanup following the “monster” Cyclone Debbie, as the now ex-tropical cyclone brought yet more heavy rain as it worked its way through the state.

At 3am on Wednesday morning the Bureau of Meteorology downgraded Debbie out of the cyclone category to a tropical low, bringing sustained winds of 55km/h with gusts of up to 85km/h. Heavy rains were still expected as it moved south-west, with a severe weather warning in place.

On Tuesday night the Queensland premier, Annastacia Palaszczuk, predicted “shock and awe” in the state when the full extent of the devastation wrought by the cyclone was revealed.

At its most ferocious the cyclone downed trees, stripped buildings and left shorelines swamped after making landfall as a category four storm at midday on Tuesday near Airlie Beach.

The storm was downgraded to a category three cyclone just after 3pm, but strong winds continued to lash Airlie Beach, Proserpine and Bowen late in the afternoon.

The state’s premier and police commissioner issued grave warnings to residents.

The premier, who on Monday warned it would be a “monster”, said the state would be dealing with the impact of the “scary” cyclone for the next three to five days as it moved down the coast.

“I think there is going to be a lot of shock and awe in the morning,” she told Ten News on Tuesday.

She said rapid assessment teams would be sent to observe the damage at first light on Wednesday, later revealing even she was “bracing” for Debbie’s full impact being unveiled.

A man, believed to be aged in his 60s, was badly injured when a wall collapsed on him in Proserpine.

He is now in a stable condition in Proserpine hospital.

“We are going to get lots of reports of damage and sadly I think we will also receive more reports of injuries, if not deaths. We need to be prepared for that,” Commissioner Ian Stewart said on Tuesday afternoon.

The Australian defence force mobilised soldiers, vehicles, aircraft and other resources to respond to Debbie, which the Insurance Council of Australia declared a “catastrophe”.

The storm earlier pounded the Whitsunday Islands, with gusts of 263km/h recorded at Hamilton Island while the jetty at Daydream Island was virtually washed away.

More than 48,000 homes were without power across the Bowen, Mackay and Whitsunday regions and more than 400 schools and childcare centres closed.

Forecasters were also warning people to remain vigilant about damaging deluges following the cyclone, with significant rain expected down the coast towards the state’s south-east.

In Bowen, where much of the local housing was built before cyclone safety standards were introduced in the 1980s, the cyclone wrecked homes and caused “major environmental damage”, Whitsunday regional councillor Mike Brunker said.

“The last couple of hours have been frightening, actually. When it crossed the coast, it was just unbelievable,” Brunker told Guardian Australia.

“There is house damage, there are people on Facebook, different friends whose houses have been wrecked. Up near the reservoir, there’s holes in roofs, a lot of environmental damage.”

Early on Wednesday the Bureau of Meteorology said the tropical low system had moved over inland central Queensland, bringing the risk of flash flooding with up to 250mm of rainfall in a day possible.

The heaviest rainfall was expected over Springsure to Yepoon.

As the system continues moving south it could bring major flooding to Ayr, and towns along the NSW border later in the week.

Damaging winds, with peak gusts of around 120km/h, continued in the region particularly about the coast and islands and also over higher ground inland.

On Wednesday morning the strongest wind gusts were affecting areas north of about Emerald to St Lawrence.