THE heavy rainfall following cyclone Oswald which has caused widespread flooding in Queensland is forecast to hit Sydney on Monday as long-weekend holidaymakers return to the city.
Experts describe the flooding and tornadoes battering the east coast as the worst they have seen in 30 years.
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A wild weather system that caused flooding and tornadoes in Queensland is now moving through New South Wales.
The weather bureau issued a severe weather warning for parts of the state with heavy rainfall and winds of up to 140 km/h expected. Up to 300 millimetres of rain could fall in areas of Sydney over 24 hours from Monday morning.
The Queensland Premier, Campbell Newman, said central Brisbane was expected to flood on Tuesday and Wednesday but the levels will not be as devastating as they were in 2011.
If current projections play out, 3600 residential properties will be affected in Brisbane and of those, 2100 are unit dwellings where only ground floor flooding is expected. About 1250 businesses are also expected to be affected while about 50 homes are projected to be inundated in the Ipswich suburb of Goodna.
Mr Newman called in the army to help with the crisis, as Bundaberg prepared for the worst flooding in more than a century.
Two Black Hawk army helicopters were sent there from Townsville to assist with rescues.
In Queensland the State Emergency Services received more than 1050 calls for assistance on Sunday, and Queensland Fire and Rescue Service conducted 34 floodwater rescues. In NSW, the SES received more than 450 calls for assistance and four people had to be plucked from floodwaters.
The federal government vowed to step up support for disaster-hit communities. The Deputy Prime Minister, Wayne Swan, said the government would provide further Defence Force assistance at the request of Queensland leaders.
Six tornadoes that hit the Mackay and Bundaberg regions caused damage to hundreds of homes. More than 100,000 homes and businesses lost power in Ipswich, Moreton Bay, Logan, parts of the Gold Coast and Brisbane.
One man died at Burnett Heads near Bundaberg. Gympie police have also recovered the body of a 27-year-old man swept away in floodwaters yesterday. The man went missing near Widgee Creek.
There are reports police have found the body of a motorcyclist swept off a bridge along the Greenbank-Goodna Road about 11pm. Passers-by tried to help by throwing him ropes, but the man was swept downstream.
The Queensland Minister for Community Safety, Jack Dempsey, said joint federal and state disaster assistance had been extended to support the central highlands, Isaac, Mackay, Whitsunday region and Bundaberg.
Mr Newman said the Prime Minister, Julia Gillard, had offered the government's full support.
Weatherzone's senior meteorologist, Brett Dutschke, said the extreme weather was unusual.
''The extent of the rainfall and how heavy it's been would only be seen once every few decades,'' he said. ''To have a system this intense moving over such a large area with this kind of impact is really unusual.''
Motorists are advised to slow down and drive for the conditions. Authorities are urging drivers returning to Sydney to leave early or delay their journey.
Dave Wright from the Transport Management Centre said the traffic on arterial roads could double on Monday with the end of the long weekend and the Christmas holidays.
He said it was possible the Pacific and New England highways north of Newcastle would close if the rain was heavy enough. Motorists should plan their trip and check for road closures before starting out.
The system causing the wild weather is expected to pick up pace as it moves south, and head out to sea in the early hours of Tuesday morning.
But dangerous surf conditions will continue until Wednesday. The Bellinger River, west of Coffs Harbour, flooded on Sunday afternoon, cutting access to the town of Darkwood.
Weather experts said there was still a risk of more tornadoes along the system's path. While cyclones such as Oswald are a large-scale system spanning hundreds of kilometres, tornadoes are more localised.
Correction: The original version of this story said that a person was missing after being swept into Traveston Dam near Gympie. In fact the missing person was a young woman last seen driving into floodwaters at Pacific Haven near Maryborough.
Sydney weather statistics can be seen here.
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