Premier Campbell Newman has assured residents the floods will be nothing like those two years ago that swept across Queensland, killing 35 people and leaving a $6 billion reconstruction task.

However, many people in the towns of Grantham and Laidley are fleeing their homes, fearful of a repeat of the floods that claimed so many lives in January 2011.

Many of the communities hit hardest in the 2010/11 floods have been inundated again and pummelled by tornadoes generated by the remnants of ex-tropical cyclone Oswald.

As the intense weather system continued to track south on Sunday evening, the weather bureau warned of minor floods in the Brisbane and Bremer rivers.

Brisbane is expecting a 2.6 metre flood peak, nearly half of the 4.46 metre peak in 2011. There will likely be two flood peaks in Brisbane at noon on Tuesday and again at noon on Wednesday.

Meanwhile, floodwaters are expected to peak in Ipswich about midnight on Monday. The Ipswich peak is expected to be about 14 metres, almost five metres below the 19.4 metre peak in 2011.

If current projections play out, 3600 residential properties could be flooded in Brisbane.

Lord Mayor Graham Quirk said of those, 2100 would likely be unit buildings. He said 1500 detached homes and 1250 businesses also stand to be affected.

Flood maps will be released on Sunday night and will include a list of affected suburbs.

But Mr Newman has stressed it will be nothing like the devastating floods of 2011.

Police Commissioner Ian Stewart confirmed the state’s first flood death on Sunday afternoon - an elderly man in the tornado-hit central Queensland city of Bundaberg.

The body of the 81-year-old man, who had been tending to his yacht, was recovered from waters in Burnett Heads.

There are still grave fears for a young man and woman missing in floodwaters, as well as a fisherman missing since Thursday night.

The young woman last seen driving into floodwaters at Pacific Haven near Hervey Bay on Sunday.

A 27-year-old man was swept away when he and two companions drove into flood waters at Widgee Creek near Gympie on Sunday morning. His two companions were rescued.

And a fisherman has been missing off Port Alma near Rockhampton since Thursday night.

Rescuers were still trying to reach three families stuck on the roofs of their homes near Gympie on Sunday evening.

Mayor Ron Dyne said the families at Widgee, between Gympie and Murgon, had been stranded for more than seven hours, but all attempts by the State Emergency Service to reach them had failed.

With much of central Queensland already under water, the southern community of Gympie is due to flood for the third time in three years. And Maryborough is also expected to go under.

In Bundaberg alone, 400 properties are expected to go under, many of them the same ones that faced a heartbreaking clean-up just two years ago.

Entire suburbs have been evacuated as flood waters continue to rise in the city. A disaster has been declared giving authorities the power to force evacuations, if necessary.

The low pressure system swept over the Sunshine Coast on Sunday afternoon, causing localised flooding and eroding the area’s famous beaches.

It was moving towards Brisbane on Sunday, where the worst of its effects are expected to be felt after dark, before hitting the Gold Coast.

Weather forecasters are warning tornadoes, like the six that caused widespread damage in the Bundaberg region on Saturday and Sunday, could also hit the southeast corner over the next 12 to 24 hours.

Deputy Prime Minister Wayne Swan promised Queensland would have the full resources of the defence force at its disposal, and two defence choppers have already been sent to Bundaberg.

He said defence assets were also being used to rescue people stranded by floodwaters at Baffle Creek, north of Bundaberg.

There have been dozens of other rescues across the state in the past 24 hours, including a woman in the Wide Bay area who was found clinging to a log in flood waters.

She had been in a boat with her husband when it overturned. The husband managed to make it to safety on his own.

There was a dramatic rescue off the Dawson Highway in Biloela, where two women and a 14-month-old baby boy became trapped on the tray of their ute on Saturday afternoon.

When the crew of the RACQ Capricorn Rescue 300 helicopter realised they did not have a sling small enough for the baby boy, they decided to put him in a sports bag to winch him to safety.

He reached the helicopter distressed and crying, but unhurt. The women were also winched to safety.

With potentially deadly conditions expected to continue into Monday, Police Minister Jack Dempsey was blunt, telling Queenslanders not to let stupidity cost someone a life.

‘‘I have swift water rescue crews still going to unnecessary people who are playing in creeks and drains,’’ Mr Dempsey said.

‘‘We have police attending and being taken away from other emergency issues because of people simply going out sightseeing and looking at areas.

‘‘Let police and other emergency services and our hardworking volunteers get on with the job of looking after their communities."

On Sunday afternoon, almost 80,000 people were without power in the southeast corner alone.

Prime Minister Julia Gillard said every avenue of assistance would be offered to the state, after the Insurance Council of Australia declared a catastrophe for large parts of Queensland.

With the extent of the damage still unfolding, ICA chief executive Rob Whelan said a catastrophe declaration meant an industry taskforce would help coordinate the response.

‘‘Insurers are greatly concerned about extreme weather expected over the next few days in Queensland, with severe inundation already having been experienced in several towns and cities, and major flood warnings now in place for every river from Cairns to the border,’’ he said.

‘‘Unfortunately, this catastrophe declaration is the result of the first cyclone to come close to the coast this season, and the weather bureau has warned it’s highly possible we will see more before the end of summer.’’

- with AAP