?Unexpected? floods in Queensland leave 15 missing as ex-cyclone Seth wreaks havoc

Parts of Queensland are experiencing major flooding, with the aftermath of ex-tropical Cyclone Seth causing "unexpected" prolonged heavy rain and storms.

The Bureau of Meteorology said there was major flooding in the Wide Bay and Burnett regions, north of Brisbane, causing highways to close and cutting off some towns.

Marodian near Gympie received more than 670mm in the 24 hours to 9am with many other areas receiving at least 300mm.

The Bruce Highway reopened late Saturday morning after the downpour forced it to close earlier.

There were warnings for more heavy rain on Saturday and authorities issued an emergency alert for Maryborough, urging people to reconsider travel.

Queensland Police confirmed one person had drowned after his vehicle became submerged in flood waters at Kanigan, Wide Bay on Friday night.

Police and emergency services responded to reports of a ute being swept off the road on Cherry Tree Road near the Bruce Highway about 7.30pm.

The driver, a 22-year-old Sunshine Coast man, was found inside the vehicle on Saturday morning. No one else was in the car at the time.

Police had been called to rescue 23 people in 11 vehicles. Eight of those were now safe, but the remaining 15 people were unaccounted for with rescue crews unable to access many areas.

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The RACQ Lifeflight helicopter released vision of it winching a family of three to safety from the second storey of their flooded home in Wide Bay, after they were trapped by the rising flood waters.

Elsewhere, Channel Seven reported that a woman and her dog were rescued from the flood waters outside Bundaberg, on Bingera Siding Road.

An elderly couple were the first to be winched to safety, followed by their son aged in his 20s.

The Queensland premier, Annastacia Palaszczuk, said the flood event was unexpected.

"As the bureau said with this severe weather event, no one was expecting it to sit and stay and produce thunderstorms that were not moving.

"This was an unexpected event from the bureau's point of view and they were sending out information as it came to hand. And also, alerting the mayors in the local council as well."

A spokesperson for the Bureau of Meteorology said the weather was extremely rare. Storms rarely sit in the same region for such a long period of time, the bureau said.

"This was incredibly rare," the spokesperson said.

"The magnitude of what we saw really escalated during the night. It was a really evolving situation."

State Emergency Service officials received more than 700 calls for help, while 31 swift water rescues were launched.

Assistant Emergency Services Commissioner Stephen Smith said his crews remain in high demand.

"Incidents are still being responded to," he said.

"Out of those 31 Swift water incidents, 18 remain open. We are having difficulty with access both on land and in air so we do urge community support in minimising to essential travel only."

Wild storms have also lashed Victoria, bringing large hail stones and flash floods.

The Victorian State Emergency Service received 848 calls in the 24 hours to Saturday, mostly due to flooding and building damage overnight.

The SES duty officer, Geb Abbott, told ABC Radio about a dozen cases were people calling to be rescued.

"There were some events where rescues had to be enacted just with people that had been stuck in flood water," she said.

The storms had left hundreds of properties without power across the state's west.

On Friday, the storms caused flash flooding in parts of Melbourne's western suburbs and the roof of a shopping centre in Point Cook caved in, collapsing under a heavy downpour.

The wild weather had already hit Portland on Thursday night, bringing down trees, damaging buildings and causing flash floods.

Additional reporting by Australian Associated Press.