Serious flooding across Australia halted mining operations and forced officials to declare a number of disaster areas as deadly wildfires raged on in the south on Wednesday.

Global mining giant Rio Tinto said its iron ore operations in Western Australia had been significantly disrupted by torrential rains and floods as a tropical low hit the region.

"Many roads are impassable and all employees have been advised to exercise extreme caution," Rio said in a statement to the Australian Stock Exchange, announcing the suspension of several projects.

In the east, parts of New South Wales were declared natural disaster zones after heavy storms spawned floods that severed roads and left towns isolated. The declaration opens the way for government assistance.

The drought-stricken town of Bourke was drenched by 200 millimetres of rain (eight inches) -- about two-thirds of its annual rainfall -- in just 15 hours. Officials put the damage bill at about six million dollars (3.9 million US).

Areas north of the state capital Sydney, Australia's largest city, were also declared a disaster zone, with the swollen Bellinger river cutting off the town of Bellingen.

Meanwhile, parts of neighbouring Queensland state were still under water after cyclonic rains flooded more than one million square kilometres (386,100 square miles).

The towns of Normanton and Karumba have been cut off by floodwaters for six weeks, and farmers estimate that between 100,000 and 150,000 cattle have perished.

The latest floods come less than two weeks after a record heatwave hit Victoria, sparking wildfires which killed at least 200 people. Thousands of firefighters are still fighting five blazes in parts of the state.

Authorities have put the cost of Queensland's floods at 210 million dollars, with 3,000 homes affected and hundreds of people forced to evacuate.