"Once-in-a-century" floods have turned streets into rivers and forced thousands to abandon their homes in northeast Australia, with authorities warning of tornadoes and more rain over the next few days.

Australia's tropical north experiences heavy rains during the monsoon season at this time of the year, but the recent downpour has surged far above normal levels.

Thousands of residents in the city of Townsville in Queensland were without power and cut off by flooded roads.

More severe weather could whip up tornadoes and destructive winds in the days ahead, Bureau of Meteorology state manager Bruce Gunn told reporters.

Up to 20,000 homes are also at risk of being inundated if the heavy rains continue.

Military personnel were delivering tens of thousands of sandbags to affected locals, as Queensland Premier Annastacia Palaszczuk warned residents to be careful.

"It's basically not just a one in 20-year event, it's a one in 100-year event," she told reporters yesterday.

The Bureau of Meteorology said a slow-moving monsoonal trough was sitting above Queensland, with some areas expected to receive more than a year's worth of rain before conditions ease.

Bureau meteorologist Adam Blazak told AFP the heavy downpours could continue until Thursday, while floodwaters would take some time to recede even when the rains lessen.

The region receives an average of some 2,000mm of rain annually but some towns were already on track to pass that.

The town of Ingham, north of Townsville, received 506mm of rain in 24 hours between yesterday and today, of which 145mm fell in just one hour, Mr Blazak said.

"I've never seen anything like this," Townsville resident Chris Brookehouse told national broadcaster ABC, adding that his house was flooded with water more than one metre deep.

"The volume of water is just incredible. Downstairs is gone, the fridge and freezer are floating. Another five or six steps and upstairs is gone too."



Mr Blazak said that with adverse weather predicted to continue for up to 72 hours, some regions could see record-breaking levels of rainfall.

There has been a silver lining to the deluge, with drought-stricken farmers in western Queensland welcoming the soaking.

"It is a welcome relief, especially in our western communities, to not only get the rain but also to fill up their dams," Ms Palaszczuk said.

"We're getting food supplies in there. We still have many roads that are cut around those areas."

The deluge comes amid a severe drought in the eastern inland of the vast Australian continent, including parts of Queensland state, that's left graziers struggling to stay afloat.

Extreme heatwaves during the southern hemisphere summer have also led to maximum-temperature records being broken in some towns.

High temperatures are not unusual in Australia during its arid southern hemisphere summer, with bushfires a common occurrence.

However climate change has pushed up land and sea temperatures and led to more extremely hot days and severe fire seasons.

In the southern states of Victoria and Tasmania, firefighters in recent days have been battling numerous bushfires threatening homes and communities.