The category two storm is now expected to make landfall by Friday evening near Brisbane, Australia's third-most populous city, the Bureau of Meteorology said in its latest update, compared with a prior projection of a landfall by early Friday.
But the storm's destructive reach will stretch across the border regions of the states of Queensland, where Brisbane is, and New South Wales, bringing heavy rain, flooding and damaging winds affecting millions of people.
"It has slowed up somewhat, that (landfall) will now be at a later time," Prime Minister Anthony Albanese told reporters on Thursday.
"That is not all good news. The risk is that in slowing up, (the cyclone) increases in its intensity but at this stage it is still predicted to be category two as it crosses onto land."
Albanese said heavy-lift helicopters had been deployed and offered to "provide whatever resources are required" for state governments.
Storm warnings on Thursday stretched for more than 500km across the northeast coast, as giant seas whipped up by the cyclone eroded beaches and officials urged residents in flood-prone areas to evacuate soon.
Cyclone Alfred stalled off the coast overnight, said Dean Narramore, forecaster at Australia's weather bureau.
Narramore said the stalling could result in "a longer and prolonged period of heavy rainfall, particularly in northern New South Wales" leading to life-threatening flash flooding.
Heavy rain from the weather system has already drenched some regions before the cyclone's landfall, Narramore said.
Total rainfall from the event could be as much as 800mm in some regions, more than the average total for March and could cause life-threatening flash flooding, the Bureau of Meteorology said.
Alfred has been called by officials a 'very rare event' for Brisbane, Queensland's state capital, with the city last hit by a cyclone more than half a century ago in 1974. The city of around 2.7 million had near-misses from cyclones in 1990 in 2019.
"This is a very rare event for south-east Queensland ... it has been many decades since this part of the state experienced (a cyclone)," Queensland Premier David Crisafulli told reporters.
He called on residents to heed evacuation orders. "If you are in a storm tide zone or you're in an area where you know there is riverine flooding, you really need to consider and think about your evacuation plan now."
Sara Robertson and her family has moved all their valuables from their home in the rural town of Murwillumbah to a motel ahead of the storm.
"I'm glad we've got a little bit more of a breather, feeling very tired today and we still have a lot to do," Robertson told ABC News after moving computers and electronics into the motel.
About 4000 properties in the rural town of Lennox Head, about 750km north of Sydney, are without power after snapped tree branches fell on power lines, NSW Premier Chris Minns told ABC News.
Qantas and Virgin Australia have cancelled several flights into Brisbane, the airport's website showed, though the airport remained open. Airport terminals at the tourist city of Gold Coast and Ballina have been closed.
Hundreds of schools in southeast Queensland and northern NSW were closed on Thursday, while public transport in Brisbane has been suspended.
The Ladies European Tour co-sanctioned WPGA Championship event was called off and the Australian Football League has postponed two matches in southern Queensland.
