Swiftwater crews are on standby in St George in Queensland's southern inland, with dozens of homes in low-lying areas at risk of flooding from the rising Balonne River.

Key points: The Balonne River at St George is expected to peak on Thursday following recent heavy rain

The Balonne River at St George is expected to peak on Thursday following recent heavy rain Floodwaters are forecast to affect about 20 homes, with residents told to evacuate

Floodwaters are forecast to affect about 20 homes, with residents told to evacuate Sunwater says it is closely monitoring the flow of water at St George but has no safety concerns

Sunwater southern region general manager John Kelly said they were closely monitoring the flow of water through the Jack Taylor Weir at St George.

"We open the gates in stages to manage the flood coming through the weir, but once the flow gets up above 60,000 megalitres a day, all the gates are open, so at the moment all 13 gates are fully open and we're discharging around 150,000 megalitres a day through the weir," Mr Kelly said.

"At this stage, we think the peak will be around Thursday morning at around 200,000 megalitres a day from the dam and that will transfer through to Jack Taylor Weir about six or seven hours later in St George."

The floodwaters are expected to affect about 20 houses. ( AAP Image: Dan Peled )

Sunwater carried out major works on the Beardmore Dam in the middle of last year, but Mr Kelly said he had no concerns about its safety.

"We're conducting surveillance around that area four times a day and we've had some of our engineers inspect the area as well and everything is holding up very well," he said.

The Bureau of Meteorology (BOM) said the river was expected to peak at 12 metres tomorrow afternoon following recent heavy rain.

"At this stage, it's still 10.5 metres approaching 11 metres … it's going up as all the water is coming from the north," senior BOM forecaster Gabriel Branescu said.

An emergency declaration is in place around the town, with residents told to evacuate and the Andrew Nixon Bridge closed.

Water makes its way down the Balonne River, forcing the closure of the Andrew Nixon Bridge. ( AAP Image: Dan Peled )

Balonne Shire Mayor Richard Marsh said the floodwaters were expected to affect about 20 houses.

"There will be water getting into the bottom of some of the homes," Cr Marsh said.

"They've all been raised so there will be no real damage to property.

"It'll get a little bit muddy … but from the point of view of homes being damaged, it won't get into the residential areas at all."

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St George resident and farmer Rod Avery spent yesterday helping friends empty their garage and prepare for their backyard to flood.

"Everyone's doing the same thing, trying to help one another out, get things up high," Mr Avery said.

"These guys have got to move out, but with a bit of luck they won't have too much water up where they have to worry about.

"Compared to the last floods, this is a lot more calmer … we've got a fairer idea of what water is coming."

Emergency services deployed four extra swiftwater rescue crews to the area and SES volunteers visited residents to tell them to prepare to evacuate.

Acting Regional Manager David Bennet said the SES was running medical supplies from Roma to towns north of St George already cut off by floodwaters.

"The flood boat operators around the Maranoa are currently assisting pharmacists in resupplying their pharmaceutical requirements for the elderly," Mr Bennet said.

"They're also doing resupplies to outlying properties."