The Balonne River was already at a record 13.26 metres on Saturday afternoon when the weather bureau predicted it could peak at 13.5 metres - the highest level since recordings began in 1890.

About 40 of the town's 2800 residents were evacuated to a makeshift evacuation centre at the showgrounds. Residents from an aged care facility in the town, 500 kilometres west of Brisbane, were flown to the state capital.

Many St George residents, including Nationals Senator Barnaby Joyce, whose family home fronts the Balonne River, spent the day filling 4000 sandbags.

About 25 homes went under but the community appeared to be spared the worst last night.

''Nobody wants to spend the next couple of months with the smell of rotting carpet and underlay around their house,'' Mr Joyce said.

The flood peak will reach the Whyenbah and Dirranbandi area during the weekend.

Residents of the Banana Shire were also urged to prepare for possible evacuation due to predicted flooding in the area.

Heavy rain has hit the towns of Theodore, Moura and Baralaba, west of Gladstone, over the past week. Emergency Management Queensland asked residents to prepare for flooding in coming days.

"Theodore could become isolated and there is the possibility that low-lying homes will be inundated,'' the Banana Shire deputy mayor Maureen Clancy said.

Further south, residents of Cunnamulla braced themselves for a drenching more severe than the floods of 2008 when waters peaked at 9.91 metres. Cunnamulla is expected to be hit with a major flood peak of 10 metres early this week.

An area greater than that of the state of Victoria has been affected by the flooding in Queensland's south. In Melbourne, hail blanketed the city like snow as a thunderstorm ripped through the capital, forcing the cancellation of major events and damaging dozens of buildings. A total of 26 millimetres of rain fell in less than an hour, bringing emergency services to a grinding halt.