Australian authorities say a body has been found in floodwaters and 13 military workers injured in a vehicle crash as wild weather from a tropical storm lashes the country’s eastern coast.

Cyclone Alfred, which was downgraded to a tropical low on Saturday, made landfall near the Queensland capital city of Brisbane in the evening local time.

Officials have warned residents to stay indoors and remain vigilant, saying the storm’s threat is “not over”.

Winds have brought down trees and power lines and flooded low-lying roads. More than 300,000 properties are without power in the region.

Police said on Saturday they had discovered a body in the search for a 61-year-old man who went missing on Friday after his car was caught in floodwaters in Dorrigo, northern New South Wales (NSW).

Emergency responders witnessed the man escaping his car and climbing onto a tree near the riverbank, but rescuers were not able to reach him before he was swept away.

Police found a body in the area on Saturday and said it “is believed to be that of the missing man”.

In a separate incident on Saturday, 13 military personnel were injured in a convoy crash in Lismore, about 200km south of Brisbane, according to Federal Defence Personnel Minister Matt Keogh.

One truck overturned while driving on a narrow road. A second truck then collided with it.

The state’s ambulance service had earlier said it treated 36 people in the accident. Keogh clarified to media that while around 36 people were involved, only 13 were injured.

They had been part of military crews deployed to Lismore, near the Queensland border, to help rescue and response operations.

“Our ADF [Australian Defence Force] heroes were on their way to help Australians in need,” Prime Minister Anthony Albanese said in a statement noting some had been “seriously” injured.

Albanese earlier on Saturday had addressed the nation from the capital Canberra, saying millions of residents were “well-prepared” but “we must remain vigilant.”

Four million people across Queensland and northern New South Wales were bracing for the storm’s landfall with dozens of weather warnings in place across both areas.

Around 287,000 customers are experiencing outages in south east Queensland, according to energy provider Energex, while Essential Energy said more than 42,600 homes and businesses in New South Wales had experienced blackouts.

People in Brisbane, Queensland’s capital, went to bed on Friday bracing for strong winds and heavy rain.

They woke up on Saturday to learn that the cyclone had been downgraded and the city would escape the worst of the weather.

But the danger’s not over in other parts of southeastern Queensland and northern New South Wales.

Along the Gold Coast, pummelled by bad weather the past few days, conditions have been very strong with driving rain and strong winds.

Hundreds of trees have been blown over in gardens, parks and along the main roads. There has been lots of debris and emergency services had sectioned off areas most at risk.

“This emergency is not over,” said New South Wales state premier Chris Minns, adding that it was “crucially important” the public did not “dismiss” the storm.

“It really doesn’t matter to us whether it’s been downgraded from a tropical cyclone to a weather event,” he said.

The state’s emergency service operations commander, Stuart Fisher, warned people not to be “complacent” and said authorities in the region expect flooding to continue over the next few days.

As the storm has edged closer to landfall, nearly 1,000 schools have closed, public transport has been suspended and airports are shut. Elective surgeries have also been cancelled.

Flights are not expected to resume until Sunday at the earliest.

The BBC spoke to several people from Brisbane’s homeless community, who took refuge at Emmanuel City Mission, which had become a round-the-clock shelter.

At the Treasure Island Holiday Park in the Gold Coast, just north of Surfer’s Paradise, a gum tree had come down between two cabins, damaging a third. Nearby, a boat was half submerged in one of the canals a block away from the beach.

On the coast itself, many paths down to the beach are now unpassable. Instead, there’s a sudden drop to the ocean where the powerful waves have eaten away at the sand.

But the clean-up operation won’t happen for a few days – the wind is still powerful and there’s driving rain.

Residents are starting to venture out to look at the damage, but plenty are remaining indoors to keep themselves safe.

With reporting by Simon Atkinson on the Gold Coast