Coastal regions from K'gari (Fraser Island) to northern New South Wales can expect heavy surf and dangerous winds over the coming days as ex-Tropical Cyclone Seth continues to sit off the Queensland coast.
All beaches were closed on the Gold Coast on Monday morning, with hazardous conditions persisting.
The system formed into a cyclone on New Year's Eve, but was downgraded to a tropical low overnight.
Bureau of Meteorology forecaster Helen Reid said its impact had coincided with king tides in south-east Queensland, making the surf conditions even more treacherous.
"It has transitioned to a subtropical system which has slightly different characteristics, but the intensity hasn't decreased," Ms Reid said.
"It's still a weather system that we need to take great care around and yes, it is still creating a difficult situation along quite a big stretch of the coast stretching from K'gari Island down across the New South Wales border."
Ms Reid said wind gusts up to 100 kilometres per hour could be expected along the coast and further inland along the Scenic Rim, while most rain from the system is expected to hit northern New South Wales.
Most beaches on the Gold and Sunshine coasts were also closed on Sunday.
Eight children were rescued by volunteer surf lifesavers at Currumundi Beach on the Sunshine Coast after massive swell turned what is usually a calm estuary into deep and fast-moving waters.
Visibly frustrated lifesavers pulled the children from the water after they ignored repeated warnings, with a cluster clinging onto flimsy bodyboards.
Members of the public jumped into the treacherous water to assist the volunteers.
Sonya Gelman witnessed the rescue and described it as incredible.
"Of course they were warning people to not swim there but no-one listened. Then eight kids got pulled out of the water," she said.
The beach was closed with large swell, king tides, and strong winds battering the area.
Surf Life Saving Queensland has urged people to avoid beaches with red flags.
Police Commissioner Katarina Carroll urged people at beaches to stay out of the water if beaches were closed.
"I spent a couple of days down the Gold Coast the last two, three days and the beaches were all closed ? and still the amount of people in the water was extraordinary, with surf lifesavers constantly driving up and down the beaches to tell people to get out," Commissioner Carroll said.
"So can I please ask that you listen to authorities, that when they say the beaches are shut, they are shut."
The wild surf has broken through to cut off a section of Bribie Island, north of Brisbane.
On the Sunshine Coast, the main tourist beaches at Maroochydore and Mooloolaba also remained closed on Monday.
On the southern Gold Coast, seas reached highs of up to 6.5 metres at Palm Beach early on Monday morning.
Currumbin surf club floods, system's movement uncertain
The car park of the popular Currumbin Beach surf club flooded following the large seas experienced on the Gold Coast.
A large shipping container at the club was dislodged from one side of the car park onto the beach by the incoming tide.
A crane has been called in to move the container.
It is still unclear if the weather system will make landfall and, if so, where it will hit.
"It is expected to be just drifting slightly further west in the coming days and expected to weaken slightly as well. And with that, as it moves slightly further west, it is possible that it will cross the Queensland coast," Ms Reid said.
"We're not sure exactly where but hopefully people will be ready for it."
More than 500 sandbags have been issued on the Gold Coast across the weekend to help with localised flooding.
Many people have gathered at points along the Gold Coast shoreline to watch the large waves rolling in.
'Extreme' heatwave conditions building
The weather system is also expected to bring thunderstorms through the north and into the Gulf country.
"We are expecting to have heatwave conditions continuing and developing and becoming more intense extreme through large parts of Queensland over the coming days," Ms Reid said.
"In the northern parts, we're expecting extreme heatwave conditions building.
"We're looking at temperatures that are going to be well over the 40s."
Mount Isa is expected to reach a top of 43 degrees Celsius today, with most parts of the central west and north west over 40C.
© ABC 2022
23:34 AEDT Severe thunderstorms are expected to lash eastern parts of the state today as Victoria continues to count the cost after days of wild weather.