RMS said at least 50 percent of economic loss is expected to come from flooding in New Orleans, hurricane losses from wind and coastal surge, infrastructure damage and indirect economic impacts.

The estimate is separate from estimates of insured losses. RMS has projected up to 25 billion dollars in losses covered by insurance, and other estimates have varied.

RMS, a consultant for insurers, reinsurers and other financial institutions, said the New Orleans flood "has developed into the most damaging flood in US history."

It said at least 150,000 properties have been flooded, topping the previous US record from flooding and levee failures on the lower Mississippi River in 1927, which affected 137,000 properties.

"The economic and insurance consequences of the 2005 Great New Orleans Flood will depend highly on how quickly authorities can respond to the event," said Laurie Johnson, vice president of technical marketing at RMS.

"The speed at which existing pumps are reactivated and additional pumping capacity is added will determine how rapidly the floodwaters are removed.