Houses have been evacuated in a rural Queensland town as rising floodwaters shut a main highway and run across the top of a bridge.

About 35 homes are threatened by floodwaters in the town of St George, about 500 kilometres west of Brisbane.

With floodwaters expected to continue rising throughout the week, residents of four of the homes have already evacuated. Others are intending to stay until the power is cut.

The Balonne River, which runs through St George, is expected to peak at about 12.5 metres on Thursday.  That is a level it has not reached since a significant flood in 1950.

By Wednesday afternoon, the water had already risen to about 11 metres. It was flowing over the Andrew Nixon bridge, which connects communities in regions west of St George.

John Kelly, the regional manager for water authority Sunwater, said the flow of water through the Jack Taylor Weir at St George was being closely monitored.

“We open the gates in stages to manage the flood coming through the weir,” he said.

“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.”

He said the weir was being closely monitored as the floodwaters rose.

The flood peak is expected to stay until Friday before slowly falling, local Mayor Richard Marsh said.

“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.”

A flooded playground in St George on Wednesday. Photo: AAP

St George resident and farmer Rod Avery spent Tuesday 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 told the ABC.

“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.”

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

But as St George prepares for floods, drought-stricken farmers just down the road have barely received a drop of rain.

Farmer Sandy Southern has been cut off but is still hoping for more rain in a region that has been in drought since 2013.

Her 13,000-hectare property has had less than 70 millimetres of rain in the past two months – while some neighbours have enjoyed up to 200 millimetres.

“If you go five kilometres east of our driveway, it is beautiful green grass. You come back to our place and it is desert,” Mrs Southern said.

“We haven’t had the yearly-average rainfall since 2011.”

The river flooding is expected to hit the town of Dirranbandi – about 100 kilometres south of St George – on Friday.

Brendan Sweeting, who is manager of The Dirran Pub, said there was a positive attitude in the town, which has been crippled by drought in recent years.

“They are all pretty upbeat here because it has been so dry for so long,” Mr Sweeting said.

He said farmers are talking about what they are going to plant, rather than wondering when rain will come.

The floodwater could take days or even weeks to flow down stream, according to the Bureau of Meteorology’s Alex Majchrowski.

He said the water was not expected to flow over the border into NSW until early March.

The Balonne River flows into the Murray-Darling system.

-with AAP