Australian troops were seriously injured Saturday in a major road crash while responding to ex-Cyclone Alfred, which has battered a swathe of the eastern coast and cut power to more than 330,000 properties.

The former tropical cyclone — now downgraded to a tropical depression — made landfall in the late evening over Bribie Island on the Queensland coastline after lingering for days offshore.

The weather system has whipped up gale-force winds that toppled trees, brought down power lines, and damaged buildings.

And it is still creating heavy rainfall, swelling rivers in parts of a 400-kilometre (250-mile) stretch of the coast straddling southeast Queensland and northeast New South Wales, government forecasters said.

Near the flood-prone New South Wales city of Lismore, two Australian Defence Force (ADF) trucks deployed to help the community were involved in a crash, resulting in 36 injuries — some serious, government officials and emergency services said.

Patients were transported to four hospitals.

"Right now our focus is on the welfare of those involved and their families," Prime Minister Anthony Albanese said.

"Our ADF heroes were on their way to help Australians in need," he said in a joint statement with the defence minister.

A 61-year-old man's body was found earlier in the day after his four-wheel drive pick-up truck was swept off a bridge into a river in northern New South Wales.

He had clambered out of the vehicle and tried in vain to cling to a tree branch in the river before disappearing into the rapid waters on Friday, police said.

Mass blackouts

The prime minister warned people not to underestimate the threat posed by the wild weather.

"While it has been downgraded, very serious risks remain so it is important that people do not take this downgrading as a reason for complacency," Albanese said.

Utility companies said 295,000 properties in southeast Queensland and another 42,600 in New South Wales were without power, warning that floods could hamper repairs.

"That's the largest ever loss of power from a natural disaster in Queensland's history," said the state's premier, David Crisafulli, estimating that about 750,000 people had been impacted since the blackouts began.

Although the weather system "stalled and began weakening", the bureau of meteorology warned that intense rain and damaging wind gusts were a risk throughout the weekend.

"Rivers are already starting to respond to the heavy rainfall, with many Minor to Major Flood Warnings current," the bureau said in a statement.

Evacuation orders had been issued for thousands of people in New South Wales, where 30 flood rescues have been carried out over the past 24 hours, emergency services said.

New South Wales Premier Chris Minns told a news conference the emergency was not over.

"It's not over for the following reasons: The rivers are full. The rain is continuing and expected to keep falling in the days ahead. And wind conditions are very high and extreme," he said.

Paramedic Ginny Burke, 30, said she was at work when the wind uprooted a large gum tree that smashed through the house she is renting in Elanora on the Gold Coast in Queensland.

Burke told AFP she returned to her crushed home, where her sister recounted that she had heard the tree fall on Friday evening but described the calamity as "really unexciting".

"What can you do?" the paramedic asked. "It's just stuff. Everyone's safe."