Hundreds of thousands of people remain without power in Australia after a cyclone brought wild weather to the east coast.

Communities in southeast Queensland and northern New South Wales (NSW) were beginning the clean-up on Sunday after the storm caused widespread flooding and knocked down power lines and trees.

A 61-year-old man's body was recovered from floodwaters on Saturday, while in a separate incident, 12 soldiers were taken to hospital after their convoy crashed en route to rescue operations.

The storm had weakened by the time it made landfall near Brisbane on Saturday night, but Prime Minister Anthony Albanese on Sunday warned locals of the continued wild weather and risks from flooding.

"The situation in Queensland and northern New South Wales remains very serious due to flash flooding and heavy winds," Albanese said.

"Heavy rainfall, damaging wind gusts and coastal surf impacts are expected to continue over the coming days."

Cyclone Alfred had hovered for days off the country's east coast as a category two cyclone before weakening into a tropical depression on Saturday.

By Sunday evening, emergency services had conducted over a dozen rescues in Queensland and NSW - most involving people trapped by rising waters in their cars or homes. The NSW State Emergency Service reported receiving more than 6,000 calls for help.

Almost 290,000 properties in the affected regions remain without power, and energy companies have warned residents the blackouts could persist for days.

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 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.

In a separate incident on Saturday, 12 soldiers were injured in a convoy crash in Lismore, about 200km south of Brisbane, as they were on their way to rescue and recovery efforts.

The soldiers were still in hospital on Sunday, two of them in a serious condition, New South Wales Premier Chris Minns told a news conference.

"We wish a speedy recovery for all of those young soldiers," he said.

Queensland's police authorities said they had not recorded any fatalities or missing people in the state so far as a result of the weather event.