Tropical Cyclone Alfred was swirling about 550 kilometres (340 miles) east of major city Brisbane, with models showing it veering towards the mainland later in the day.
Bureau of Meteorology forecaster Dean Narramore said the storm was likely to cross the coast late Thursday or early Friday, striking land between metropolitan Brisbane and the tourist haven of the Sunshine Coast.
It would be the first tropical cyclone to make landfall in that part of Australia since 1974, Narramore told AFP.
"It's not record breaking, but it's definitely a little bit more unusual," he said.
Some three million people live along the 100-kilometre (60-mile) stretch linking Brisbane and the Sunshine Coast, a region known for its balmy weather and golden beaches.
Two opening-round Thursday night Australian rules football matches -- the country's most popular spectator sport -- were postponed to a date yet to be announced, the game's bosses said.
Australian Football League chief executive Andrew Dillon said the priority was to "do everything we can to ensure the health and safety of everyone" in impacted areas.
- 'Flash flooding' -
Climate researcher Tom Mortlock said unusually warm sea surface temperatures were fuelling the storm.
"Tropical Cyclone Alfred is a reminder that tropical cyclones... can still track further south," he said.
Researchers have repeatedly warned that climate change amplifies the risk of natural disasters such as bushfires, floods and cyclones.
Tropical Cyclone Alfred, a category two system, would lash the coast with "damaging" 120-kilometre (75-mile) per hour winds, official forecasts said.
There was also the risk of "dangerous and life-threatening flash flooding".
The rescheduling of two Queensland matches -- Brisbane against Geelong in Brisbane, and Gold Coast against Essendon on the Gold Coast -- left just two opening round fixtures to be played in Sydney on Friday and Sunday.
A Women's Professional Golf Association event and the Gold Coast Festival of Golf were cancelled due to the "impending impact", organisers said on Tuesday.
Australia's second-largest triathlon was also called off.
While cyclones are common in the warm tropical waters lapping Australia, it is rare for them to strike the heavily populated areas found further south.
The flood-prone northern rivers region of New South Wales, which lies south of Brisbane, would also feel the impact, officials said.
New South Wales Premier Chris Minns urged towns to "be prepared for the worst".
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