Southeast Queensland and northern NSW have borne the brunt of the heavy rain so far, with 241mm falling on Doon Doon and 182mm on Mullumbimby in the 24 hours to 9am on Friday.
Heavy rainfall in southeast Queensland has prompted fears of flash flooding, dangerous road conditions, power outages and transport delays.
Millions are set to be impacted across the heavily populated area that includes Brisbane, the Gold Coast and the Sunshine Coast.
Bureau of Meteorology senior meteorologist Angus Hines said rain would "continue to accelerate" late on Friday.
"It does look like the south-eastern corner will continue to pick up the heaviest falls, much like we have already seen through the course of the last 24 hours," he said.
In Queensland, further heavy falls were possible up into the Wide Bay-Burnett region and inland to parts of the Central Highlands and out towards the western districts.
"This is not a one-and-done weather event," Mr Hines said.
"Once we push into the weekend, it's up through inland parts of central and even northern Queensland where we anticipate those heaviest falls on Saturday and again on Sunday."
Many areas could expect falls of 100 to 150mm, "so it will be an extensive wet weather weekend all the way from the north of Queensland down to the southeast", Mr Hines said.
"With all this rain coming in over the next two to three days, we will see weather impact primarily in the form of flooding.
"Flash flooding and riverine flooding remain possible."
Queensland has been reeling from wild weather in the north, with communities isolated and livestock devastated after widespread flooding following ex-Tropical Cyclone Koji.
More rain could also threaten the Northern Territory after storms turned the usually dry Todd River into a raging torrent, triggering multiple rescues in Alice Springs.
One woman washed into floodwaters spent 11 hours clinging to a tree before rescuers finally reached her.
The Todd River flooded low-lying roads and closed all causeways across the riverbed on Thursday after up to 100mm of rain fell in the catchment in just two hours.
Authorities responded to people stranded in floodwaters, vehicles becoming stuck, and reports of inundated homes.
The Todd River began to recede on Thursday but locals have been urged to "stay vigilant".
"It is at a watch and act situation. We do anticipate further rainfall," NT Police Southern Commander James Gray-Spence told reporters late on Thursday.
"We don't know whether it will fall in the catchment or the effect on the river, but we will pass that information on to you as soon as it happens - so stay vigilant."
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