Business owners in a southeast Queensland town are evacuating for the second time in a month with floodwaters again threatening to enter the town.

More than 170mm of rain has fallen in the Gympie region in the past 24 hours.

The Mary River is expected to peak at 18 metres on Tuesday evening, three metres above the level which causes flooding in the town's CBD.

More than 100 businesses and homes were affected when the river reached 20.3m on January 28.

This time no homes should be impacted, but it would likely hit up to 39 businesses.

Mayor Ron Dyne says the circumstances are beyond belief.

"We do have a reputation of being able to look after ourselves in flood circumstances, but this is a major impact on businesses, on farms," he told ABC News 24.

"People are starting to get really concerned about how they're going to exist, how they're going to continue on."

Panel beater Noel Edmonds said he only moved back into his River Road premises two weeks ago.

Last month, two metres of water swamped his workshop, ruining some stock.

Now he is evacuating again, the third or forth time in two years.

"It's catastrophic. We've just had enough," he told AAP, adding he couldn't afford to move the business.

"To replace this in a higher location would be worth a lot of money and we just don't have those sort of finances in our particular industry."

The Gympie Cats AFL club suffered more than $80,000 worth of damage when water rose over the clubhouse roof last month.

Club vice-president Brett Hall says the water is again over the floorboards and rising.

"It's pretty devastating to be honest," he told AAP.

"We just finished cleaning up and getting ready to go from the flood a month ago and here we go again."