Sydney: Five people have been swept to their deaths by flash flooding in northeastern Australia, officials said today, after what the Queensland state premier described as an "off-the-scale" downpour.

State Premier Annastacia Palaszczuk said in the first incident a man, woman and child died when their car was swept away by floodwaters in Caboolture, some 44 kilometres (27 miles) north of Brisbane.

"This is off-the-scale," she said of the deluge in which 277 millimetres (almost 11 inches) of rain fell in the Caboolture area in just three hours yesterday afternoon.

In a second incident, also in Caboolture, a car carrying three people was swept away but two passengers, a 21-year-old woman and a boy aged 16 managed to escape. The body of the driver, a 49-year-old man, was found early today.

Police said in a third fatal incident involving vehicles being swept away, a 75-year-old man died in nearby Burpengary but police were able to rescue a 68-year-old woman found clinging to a tree.

"It's unfortunate that with events like this, we again need to highlight to the community the dangers of entering flooded road waters. If it's flooded, forget it," Queensland Police Inspector Lee Jeffries said.

"The reports that I have is that the roads were well-and-truly flooded at the time and vehicles have entered flooded roads."

Southeast Queensland was lashed by the storm, which forced the postponement of the Australia against New Zealand rugby league Test in Brisbane.

Torrential rains closed roads, prompted dozens of rescues and cut power to thousands of homes.

The weather bureau said today that the worst of the storm was over for Queensland, and the weather was weakening as it moved south into New South Wales state.

"Apart from still some pretty wild surf conditions along the coast, apart from that the event is pretty much over for us in southeast Queensland," Bureau of Meteorology spokesman Jonty Hall told the Australian Broadcasting Corporation.

New South Wales was hit by wild weather last month that left four people dead and caused millions of dollars in damage across Sydney and surrounding areas.

In that event, relentless gale force winds and torrential rain brought down trees and power lines, many crushing houses and cars, with a handful of homes washed away in what was described as a once-in-a-decade storm.