If those forced out of New Orleans by Hurricane Katrina end up re-building their lives in new locations, it could be the largest U.S. black resettlement since the Great Migration of the 20th Century lured southern blacks to the North in search of jobs and better lives.

Officials have said it will take many months and maybe even years before New Orleans is rebuilt. On Monday, Deputy Police Chief Warren Riley said: "We advise people that this city has been destroyed. We are simply asking people not to come back to this city right now."

Hurricane Katrina evacuees from New Orleans gather up their luggage after arriving at Charlotte Douglas International Airport, Monday, Sept. 5, 2005, in Charlotte, N.C. (AP Photo/The Charlotte Observer, Jeff Siner)

In Houston, which expected many thousands of evacuees to remain for a long time, interviews suggested that thousands of blacks who lost everything and had no insurance will end up living in Texas or states other than Louisiana.

Many evacuees like Percy Molere, 26, who worked in a hotel in New Orleans' French quarter, said they cannot keep their lives on hold for very long. Molere said: "If it took a month, I'd go back, but a year, I don't want to wait that long. Hopefully we're going to stay in Houston just to stay out of New Orleans" for the time being.

Experts cautioned that it is too soon to predict the long-term impact of the devastation of New Orleans, but one scenario would be massive resettlement elsewhere.

"You've got 300,000, 400,000 people, many of them low income without a lot of means, who are not going to have the ability to wait out a year or two or three years for the region to rebuild," said Barack Obama, the only black member of the U.S. Senate.

During a visit to Houston on Monday, Obama said: "They are going to have to find immediate work, immediate housing, immediately get their kids into school and that probably will change the demographics of the region."

Because of the legacy of slavery, southern states including Louisiana, Arkansas, Mississippi, Alabama, Georgia and South Carolina have historically been home to the greatest concentration of U.S. blacks. In 1900, 85 percent of U.S. blacks lived in the South and as early as 1830, more than 58 percent of Louisiana's population was black.

Between 1940 and 1970 economic changes prompted 5 million blacks to quit the south for cities across the north including Chicago, Detroit and New York, marking one of America's largest internal migrations.

But New Orleans did not always follow the trend. Historically, far fewer residents have moved from New Orleans than from most American cities, despite its high poverty and crime rates.

Nicholas Lemann, author of "The Promised Land: The Great Black Migration and How it Changed America," said it's too early to tell whether Katrina would prompt major resettlement.

Lemann said as officials accommodate large numbers of blacks in other cities, they should avoid putting them in confined areas as Chicago did in the past, which created new urban woes. He said: "They should think carefully on how to avoid the sort of ghetto phenomenon."

Part of the migration trend will be set by what federal, state and local agencies do to help refugees rebuild their lives.

"What I do think should be focused on now is what is the Congress is going to do when they get back," former President Bill Clinton said in Houston Monday. "How are we going to find jobs for these people, where are they really going to live, do they need some cash right away?" "They feel lost."