Brisbane and Ipswich are expected to flood this week, but Queensland Premier Campbell Newman says it will not be as severe as in 2011.
Torrential rainfall continues to fall across central and southern Queensland and floodwaters are predicted to inundate 3600 homes and 1250 businesses in Brisbane.
The state's south-east is also on tornado watch on Sunday night.
The army has deployed three Black Hawk helicopters to help with flood evacuations in Bundaberg, where the Burnett River has broken its banks and hundreds of homes and businesses will flood.
The ABC reports an elderly man's body has been recovered from waters at Burnett Heads, while a woman and a man are missing in floodwaters in Maryborough and Gympie.
Hundreds of Bundaberg residents are being ordered to leave their homes with forecasts predicting more rain and flooding.
Australian authorities say up to 300 homes in north Bundaberg are expected go under, and those that don't will be isolated.
A disaster has been declared giving the state the power to force evacuations, if necessary.
The ABC reports that up to 100 homes and businesses are already flooded in Bundaberg north and dozens are inundated in Bundaberg east.
Two years ago, flooding in Queensland left 35 people dead.
AAP reports that floods are also expected at Gympie and Maryborough.
Brisbane, the Gold and Sunshine coasts, and northern NSW are also on flood watch as the low pressure system that was Cyclone Oswald tracks south.
At Gympie, north of Brisbane, residents are being rescued from rooftops.
A 27-year-old man is missing in floodwaters after trying to cross a flooded creek near Gympie. Two other people were rescued but a swiftwater rescue team lost its boat in the operation.
The city's CBD is expected to flood later on Sunday as the Mary River rises towards an expected peak of 17 metres - just shy of levels reached during the devastating 2011 floods.
Further north, communities around Gladstone are seeing unprecedented flooding, with 900 homes evacuated.
Gladstone Deputy Disaster Coordinator, Inspector Les Bulluss, says a high tide combined with 8.5 metres of water going over the Awoonga Dam wall is to blame.
Boyne Island and Tannum Sands are experiencing flooding, but so far there are no reports of homes going under there.
But the news is not as good for residents at nearby Baffle Creek, where some homes have water up to their ceilings and there have been several rescue efforts.
More than 30,000 customers are without power in flood-affected parts of the state.
The Bureau of Meteorology has issued a flood warning for the Lockyer and Laidley creeks, in the Lockyer Valley, west of Brisbane.
Valley communities are still rebuilding after deadly walls of water swept through during the 2011 flood disaster.