The Queensland floods have hit businesses all across Australia, with a National Australia Bank survey estimating they cut 5 per cent off the revenue of large and medium-sized businesses.

Not surprisingly, the biggest hit was to Queensland businesses, where revenue was down 9.8 per cent and the utilisation of machinery was down 13.8 per cent.

But other states were also hit, with a 4 per cent drop in business revenue in NSW and Victoria during last month attributed to the Queensland floods.

The floods caused disruption to 10 per cent of businesses nationally, the survey found, while 25 per cent of those surveyed in Queensland had experienced some disruption or closed.

The building and construction sector was hardest hit -- although this sector stands to gain most out of the reconstruction following the floods and cyclone -- while the impact on the retail sector, agribusiness and mining were also sizeable.

The survey, conducted among 1500 businesses across Australia that had more than 50 employees, also found that 20 per cent of businesses thought they would take more than a month to recover from the floods.

Somewhat surprisingly, a parallel survey conducted by the NAB found that business confidence in Queensland was the highest of all states last month, despite the floods.

"When you're standing in your business with your feet wet in the middle of a flood, I guess the future always looks better," said NAB chief economist Alan Oster.

But the NAB also takes a more pessimistic view than the Reserve Bank of the effect of the floods on the national economy -- while the Reserve Bank estimated that the floods would cut one percentage point off GDP growth for the current quarter, the NAB estimate was that it would be closer to 1.5 percentage points.

The main economic effect of the floods will be felt in the city of Brisbane because of its larger population, and the city's Lord Mayor, Campbell Newman, said yesterday that the floods would cost the council $440 million.

But Mr Newman also declared his "pet" $1.7 billion Northern Link tunnel off-limits in the search for the $440m, saying instead it would be paid for by slashing council programs in the next two years.

"Our approach is to balance the books, find projects to cancel or defer, find internal savings . . . and then claim the maximum amount we are entitled to from the federal and state governments and our insurers," Mr Newman said.

"The ultimate net gap (for ratepayers) might be as low as $20m, but up to $50m."

The survey did not deal with the effect of the Victorian floods or the North Queensland cyclone on the national economy, but Mr Oster said he expected their impact would be less than the Queensland floods. "For people in the cyclone and directly affected by it, there's no doubt it was a catastrophic event, but the economic effects will be a lot smaller," he said. "It will mainly impact on the tourism and the agricultural sectors."

The main commodity that will be affected by the North Queensland cyclone is sugar, and Canegrowers chief executive Steve Greenwood said yesterday there would be more damage to the crop than the $500m estimated last week.