Like other disaster-ravaged areas, Louisiana and Mississippi are expected to see massive rebuilding efforts that could boost their economic growth eventually.

But unlike Florida, which is undergoing a speedy recovery from an onslaught of hurricanes last year, the two southern neighbours could find their revival much slower and tougher. That's because a recovery's speed and strength can depend on several factors, including wealth, the condition of a disaster area's infrastructure, population growth and even presidential politics.

The area hit by Hurricane Katrina has few, if any, of these factors going for it, economists said.

Florida's recovery from hurricanes last year was helped in part by the state's relative affluence and its status as a battleground in the presidential election. The state is now adding jobs at a faster pace than the nation, thanks partly to rebuilding efforts.

The San Francisco and Los Angeles areas bounced back from earthquakes in 1989 and 1994 in part because their key economic engines - including technology and finance in the Bay Area and entertainment and trade in southern California - were not severely hampered.

But Louisiana and Mississippi have two of the nation's lowest per capita incomes. And their economic engines - energy, ports and tourism - all suffered massive blows. "If you add it all up, it feels like Katrina will be the most economically costly natural disaster in our history," says Mark Zandi, chief economist for Economy.com, a research firm in West Chester, Pennsylvania.

President Bush acknowledged that on Wednesday when he said: "We are dealing with one of the worst natural disasters in our nation's history."

Still, economic activity almost always picks up after a disaster, thanks to rebuilding efforts supported by government aid and insurance, says Mark Vitner, senior economist at Wachovia, a banking company based in Charlotte, North Carolina. Stronger growth won't be hard to achieve in Louisiana - its economy has actually shrunk since 2000, he said. But that doesn't mean a devastated region will end up better off, because a lot of wealth gets wiped out, Vitner says. "Rebuilding efforts do provide a lift to measurable economic activity, but what we rarely see in the data is the immense permanent loss of wealth," he said. In the case of Mississippi and Louisiana, "the loss of wealth will severely hinder the recovery efforts."

Among key factors that can determine the economic rebound from a disaster is damage to a region's economic engines. Hurricane Andrew in 1992 inflicted severe damage to certain parts of Miami, but didn't knock out the city's key economic drivers, Zandi says.

The 2001 World Trade Centre terrorist attacks hurt Wall Street's financial infrastructure, but backups allowed trading operations to continue a few days later, says Nariman Behravesh, chief global economist at Global Insight, a consulting firm in Waltham, Mass.

No such luck with Katrina. Its economic victims of energy, trade and tourism have no alternative systems to replace them. "All three have been laid low and might remain off line for some time," Zandi says.

In last year's Florida hurricanes, electricity in affected areas was knocked out for three to four weeks, but other infrastructure was largely intact, Zandi says. The Los Angeles area suffered only a few highway closures and temporary power outages after the 1994 Northridge quake.

No such mercy from Katrina. It appears to have knocked out many of the area's major bridges, electrical systems and other key infrastructure.

Typically only 50 per cent to 60 per cent of disaster losses are insured, so people often draw on their own finances to rebuild, Vitner says. Mississippi has the nation's lowest per capita income, while Louisiana ranks 42nd, Vitner says. "That means that folks who are underinsured or uninsured won't have their own means to repair properties," Vitner said.