Heavy rain triggers flash flooding, power outage fears

Millions are set to be impacted across the heavily populated area which includes Brisbane, the Gold Coast and Sunshine Coast.

Six-hourly rainfall totals up to 90mm and isolated falls as high as 150mm have been forecast.

Queensland was already reeling from wild weather in the north, with communities isolated and livestock devastated after widespread flooding in ex-Tropical Cyclone Koji's aftermath.

The state's southeast is now bracing for what could be days of rain after the heavens opened when a cool change moved through NSW's northeast overnight.

There have already been heavy falls, particularly in NSW's northeast with 178mm recorded at Green Pigeon and 131mm in Mullumbimby.

Flood watches have been issued from Bundaberg north of Brisbane to northern NSW's Ballina, extending inland to Queensland's southwest.

The Brisbane, Logan and Albert Rivers are set to be impacted along with the Burnett, Condamine, Balonne and Dawson inland systems.

More rain may 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."