"I said thousands. Some computer models say 10,000. I don't know what the number is. But it's going to be big. And it's going to shock the nation," New Orleans Mayor Ray Nagin said on CBS News' The Early Show.
Nagin said it could take about three months before New Orleans is back in business.
"Probably three weeks to clear the water. Another couple of weeks to clear the debris. And six to eight weeks to get the electricity going," Nagin said.
The U.S. Army Corps of Engineers began pumping water out the flooded city Monday after closing a major gap in the levee that burst during Hurricane Katrina, flooding 80 percent of the bowl-shaped city.
Efforts to evacuate holdouts were stepping up Monday, with boat rescue crews from around the country searching for people to rescue.
"In some cases, it's real easy. They're sitting on the porch with their bags packed," said Joe Youdell of the Kentucky Air National Guard. "But some don't want to leave and we can't force them."
"Long as they keep bringing food and water, we can hold out 'til this water goes down," Kenny White told CBS News.
The city's police chief is begging them to come in and get out.
"There is absolutely nothing here. We advise people that this city has been destroyed. It has completely been destroyed," said Chief Warren Riley.
In the New Orleans suburbs, there are the earliest signs of returning life, reports CBS News Correspondent John Roberts. Cleanup crews are clearing tree clogged streets. The power companies are putting the lines back up. The handful of gas stations open for business have lines that last for hours. And in some places, people are beginning to trickle back home.
Draining the flood waters is likely going to take weeks, leaving behind a layer of toxic sludge — and bodies. The mayor said it wouldn't be "unreasonable" to have the city's death toll reach 10,000.
In neighboring St. Bernard Parish, officials expressed frustration that federal aid, slow to reach New Orleans, was even slower to get to outlying areas.
"This is Day 8, guys. Everything was diverted first to New Orleans, we understand that. But do you realize we got 18 to 20 feet of water from the storm, and we've still got 7 to 8 feet of water?" said Ron Silva, a district fire chief. "If you had dropped a bomb on this place, it couldn't be any worse than this."
In addition to help from other Louisiana and Alabama departments, a Canadian task force of firefighters and police arrived four days after the storm to help, St. Bernard Fire Chief Thomas Stone said.