Torrential rain over the weekend has severely flooded several cities and towns in eastern Australia, leading to three deaths in the region.

Many businesses and homes in the Queensland state capital, Brisbane, were inundated on Monday, while about 1,200 properties were flooded by record-high waters in the city of Bundaberg 385km to the north.

Helicopters were used to rescue 18 people from the roofs of their homes in Bundaberg, Australian Associated Press reported.

Queensland police on Monday confirmed that three people had died in flood waters since the weekend.

There was also flooding in the Queensland towns of Gladstone, Gympie and Ipswich.

Almost 250,000 homes across Queensland were without power on Monday and the triple-zero emergency phone network was down in a number of areas, with mobile phones also out of service.

The heavy rain was caused by the remnants of a tropical cyclone that hit the country last week and also brought severe weather including tornadoes. Several high-water rescues have taken place.

Campbell Newman, Queensland premier, said there was an acute emergency unfolding in Bundaberg, home to about 50,000 people, with many people scrambling to get out as the river hit a record peak.

'Uncharted territory'

Newman said authorities were now in "uncharted territory", with debris-laden floodwaters flowing through the town at such speeds that water evacuations were no longer viable and there were fears homes could be torn from their foundations.

More than 2,000 homes had flooded and "many thousands" of people were affected, he said, with a "significant number" of people expected to be trapped in their homes.

Up to 60 patients at the local hospital were being shifted to its upper floors.

"We are at a point where we've never seen floodwaters like this before," Newman said.

"We're very concerned that the velocity of the water and the rise in water levels means that literally houses, particularly in North Bundaberg and maybe other locations, could be swept away. This is a very real prospect."

Fourteen helicopters, including two army Black Hawks, would fly rescue missions until nightfall and, Newman said, the government was scrambling to find extra aircraft to boost efforts.

Thousands of people have evacuated their homes across Queensland, with flood warnings for the majority of the state's rivers as the former tropical cyclone Oswald sweeps into neighbouring New South Wales, bringing high winds and heavy rains.