Australia's military has been deployed to tackle devastating “once-in-a-century” floods that have inundated homes, schools and airports in the country's northeast, forcing hundreds to flee and bringing crocodiles onto the streets.

The Australian Defence Forces delivered 70,000 sandbags, deployed amphibious cargo vehicles and helped pluck flashlight-wielding residents from their rooftops Monday, as monsoon rains drenched the northern state of Queensland.

Australia's tropical north typically experiences heavy rains during the monsoon season, but the recent downpour has seen some areas get a year's worth of rainfall in a week.

The authorities were forced to open floodgates of a major dam late on Sunday, unleashing what they called “dangerous and high velocity flows.” In hard-hit Townsville, cars were mostly submerged, with picket fences barely poking through waist-deep flood waters.

“We've never seen so much water in our lives,” said local radio journalist Gabi Elgood.

“You think there can't possibly be any more to come but the rain just doesn't stop.” Desperate residents had to contend not only with flash flooding, landslides and power blackouts, but also several saltwater crocodile sightings in residential roads and cul-de-sacs.

Queensland Police issued a blunt warning for people to stay out of floodwaters.

“If the thought of coming face to face with a crocodile isn't deterrent enough, before you start playing in flood waters you should always remember the distinct possibility you could be wading in your neighbour's faeces”, the statement said.

Emergency services have struggled to respond to the scale of the disaster, with more than 1,100 people calling for help and 18 “swift water rescues” conducted overnight.

“Small boats worked through the night to evacuate members of the community,” said local commander Brigadier Scott Winter.

Around 400 Townsville residents have sought shelter at nearby Lavarak military barracks.

'Unprecedented'

State premier Annastacia Palaszczuk warned the communities face more difficulties ahead. Schools and courts remain closed, more rain and high winds are on the way and emergency warnings still in effect for more than a dozen rivers.

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

“It's basically not just a one in 20-year event, it's a one-in-100-year event,” said Palaszczuk. “This is unprecedented, we've never seen anything like this before,” she said.

Ergon Energy's spokesperson Emma Oliveri told AFP that more than 16,000 people were without power, with the supplier unable to say when the lights will come back on.

The main transport artery linking the north of Australia with the rest of the east coast was also affected, prompting concerns about food shortages.

Woolworths Northern Queensland Operations Manager Tina Anandji said the company had “secured two charter planes to carry 3,000 tonnes of fresh food and essential items” to the northern city of Cairns.

“We'll continue to do all we can to get stock into Far North Queensland while the roads are cut,” she said.

The Bureau of Meteorology's Adam Blazak told AFP the downpours could continue until Thursday, while floodwaters will take some time to recede even when the rains lessen.

A silver lining to the deluge is that it has boosted drought-stricken farmers in western Queensland.

“Queensland has already born its fair share of extreme weather recently, with unprecedented bushfires, drought, heatwave, a cyclone, and now intense rainfall and flood,” said Richard Thornton of the Bushfire and Natural Hazards Cooperative Research Centre.

He warned resources “are now being stretched beyond normal with the severe weather seasons getting longer and more complex”.