Swollen rivers burst their banks after unusually heavy downpours last week over outback Queensland, an arid region home to some of the country's largest cattle ranches.

Officials said more than 100,000 livestock -- cattle, sheep, goats and horses -- had been swept away, were missing, or had drowned.

"These are only early indications of the magnitude of this disaster and while these preliminary numbers are shocking, we are expecting them to continue to climb as flood waters recede," said state agriculture minister Tony Perrett.

"It's heartbreaking to consider what western Queenslanders will be going through over the weeks and months as they discover the full extent of losses and damage -- and start the long slog to start again."

Researchers have repeatedly warned that climate change amplifies the risk of natural disasters such as bushfires, floods and cyclones.

-- Fodder drop --

Flood waters stretched some 500,000 square kilometres (190,000 square miles) across sparsely populated western Queensland, Perrett said, a landmass roughly equivalent to France.

Industry body AgForce told local media some cattle ranches may have lost almost 100 percent of their herd.

The government Bureau of Meteorology said some towns had recorded as much as 500mm (20 inches) of rain in the space of a week -- their typical yearly total.

Muddy livestock survived by crowding together on the few small hills cresting above the flood waters, photos posted to social media showed.

Queensland's fire department used helicopters to drop bales of fodder near surviving animals cut off from food.

The state's primary industries department said some 4,000 kilometres (2,500 miles) of road had been flooded -- a distance greater than the famed Route 66 connecting Chicago to Los Angeles.

Rising waters on Tuesday morning encircled the remote outpost of Thargomindah, which describes itself as Australia's farthest town from the sea.

A makeshift dirt flood levy was dug around the town to protect its 200 residents.

- Cattle country -

"Preparations are well underway, including securing food deliveries, ensuring the airport has enough aircraft fuel and if need be an evacuation point and accommodation," the shire council said.

"Our shire's isolated properties are stocked with food and supplies and doing okay under the circumstances."

Australia's so-called "channel country" is one of the country's biggest cattle fattening grounds.

Most of the time its sweeping plains are dry and inhospitable.

But cattle gorge themselves on the pastures that sprout whenever wet season rains fill the dry creek beds -- or channels -- that snake through the region.