US President George W Bush, under fire for his handling of Hurricane Katrina, has revisited the disaster area and pledged long-term help for the region.
President Bush has acknowledged mistakes in the response
He toured Louisiana and Mississippi and declared states of emergency in 10 more states, where evacuees have arrived.
Former Presidents George Bush Sr and Bill Clinton announced a nationwide fund-raising campaign for victims.
Mr Bush has invited top US politicians of both parties to the White House on Tuesday to discuss the situation.
Meanwhile thousands in New Orleans have visited their homes to view the damage.
Long traffic queues formed on the approaches to the city as people headed home to see how badly their properties were damaged.
Mr Bush, on his second visit to the Gulf Coast in four days, pledged "a huge effort" for hurricane victims.
Speaking to emergency officials gathered in Poplarville, Mississippi, he declared: "We're here for the long term."
"I understand. I understand the damage. I understand the devastation, I understand the destruction, I understand how long it's going to take. And we're with you. That's what I want you to know," he said.
By declaring states of emergency elsewhere, he enabled federal funds to be made available to assist refugees who have arrived as far afield as Utah, West Virginia and Florida.
Meanwhile the previous two US presidents formally launched the Bush-Clinton Katrina Fund for disaster relief at a meeting in Houston, Texas.
New Orleans Mayor Ray Nagin told NBC's Today Show that a figure of 10,000 deaths "wouldn't be unreasonable".
Caked in mud
Rescuers continue to search for stranded survivors, but also for bodies, some of which are being put in refrigerated lorries and portable morgues.
Work is continuing to shore up levees and floodwalls, and to drain the standing water from the city.
The broken 17th Street Canal levee, the cause of much of the flooding, has finally been mended, and engineers are beginning to pump water from the canal to reduce its unusually high level, says BBC correspondent James Coomarasamy in New Orleans.
Some roads were reopened on Monday so that people could return briefly to their homes.
Finding his house caked in mud and mould, Gabriel Whitfield, 36, said it was like being "punched in the gut".
"It's hard to see something you worked so hard to accomplish just wiped out," he said.
Even as some evacuees were returning, Deputy Police Chief Warren Riley warned those remaining to leave.
"Our officers are basically telling people there is absolutely no reason to stay here... We advise people that this city has been destroyed," he said.
Fewer than 10,000 people remain in the city, according to an army estimate based on aerial reconnaissance.
Mr Clinton and his wife, New York Senator Hillary Clinton, have raised the idea of a 9/11 style Congressional inquiry into Hurricane Katrina and the federal government's response.
Senate Democratic Leader Harry Reid backed the idea. "Serious mistakes were made," he said.
Mr Bush has been criticised in some areas for being slow to respond to the crisis.
He has admitted some of the relief effort has been "unacceptable", but insisted: "All levels of government are doing the best they can."
However the chairman of the Democratic National Committee, Howard Dean, said the president's trip to the Gulf Coast was "another callous political move" aimed at shifting blame for the failures from himself.