Deteriorating conditions in New Orleans will force authorities to evacuate the thousands of people who sought refuge at shelters in the city, Louisiana Gov. Kathleen Blanco said Tuesday.
"We're going to try to get those people relocated as soon as we possibly can get a plan together," she told reporters.
"A lot of people lost their lives, and we still don't have any idea [how many], because the focus continues to be on rescuing those who have survived," she said.
Elsewhere Tuesday along the Gulf Coast, authorities used boats and helicopters to reach residents stranded by Hurricane Katrina and search for survivors.
The storm ripped ashore in Louisiana Monday morning with winds topping 140 mph before scourging Mississippi and Alabama.
The death toll from the storm is estimated at 68 -- mostly in Mississippi. Officials stressed that the number is uncertain but likely to be much higher.
"We know we've had some loss of life. We really don't know how much. There are credible accounts of 50 to 80 in Harrison County. Those are not confirmed, but they're credible," Mississippi Gov. Haley Barbour said.
"And I hate to say it, I think there are going to be more."
While Louisiana officials have not confirmed any deaths there, New Orleans Mayor Ray Nagin said there have been reports of bodies floating in the floodwaters. Two storm-related traffic fatalities were reported in Alabama.
Katrina caused widespread flooding across the region, and floodwaters were still rising Tuesday in New Orleans after a hole opened in a levee protecting the city.
Water poured from Lake Pontchartrain after a two-block-long breach opened overnight in a section of a levee that protects the low-lying city.
Nagin had said that about 80 percent of the city was flooded and that some areas were under 20 feet of water.
CNN's John Zarrella, in a hotel on Canal Street, said the water level was "much higher" than it had been during the height of Katrina's onslaught, rising all morning Tuesday and topping the sandbags meant to keep the water out of the building.
"Water has now filled the basement of the hotel," he said. "All of the entrances to our hotel are completely surrounded, and the water is slowly creeping up the side of the building.
"Yesterday during the hurricane, the water was nowhere near this high."
CNN's Adaora Udoji, monitoring the rescue efforts, said authorities had ferried at least 500 people from their homes, flooded with as much as six feet of water. Some residents reported water rose so fast they did not have time to grab their shoes.
A 50-inch water main break left the city without drinkable water, and the massive power outages caused by the storm are likely to take at least three or four weeks to repair.
Nagin said both the city's airports were under water, the Southern Yacht Club had burned to the ground, an oil tanker had run aground and was leaking, there were gas leaks throughout the city and Interstate 10's twin spans heading east over the lake were "completely destroyed."
The FAA hopes to open one runway at Louis Armstrong New Orleans International Airport for emergency flights.
In Mississippi, streets and homes were flooded as far as six miles inland.
Barbour plans to make a helicopter tour of the hardest hit areas today.
In Biloxi, a 25-foot storm surge crashed in from the Gulf of Mexico on Monday and inundated structures there. Up to 30 people are believed to have been killed when one apartment complex on the beach collapsed in the storm.
One man in Biloxi told CNN affiliate WKRG-TV he believed his wife was killed after she was ripped from his grasp when their home split in half.
"I held her hand as tight as I could," the unidentified man said. "She told me, 'You can't hold me.' She told me to take care of the kids and the grandkids ... we ain't got nowhere to go. I'm lost. That's all I had."
"This is our tsunami," Biloxi Mayor A.J. Holloway told the Biloxi Sun Herald newspaper, referring to the December 26, 2004, tsunami that killed more than 226,000 people in the Indian Ocean region.
Debris littered the streets and the ground floors of several structures.
Cement trash cans used as barriers in front of buildings were strewn about like cardboard boxes, and paper scraps hung from the highest branches of the trees still standing.
CNN's Miles O'Brien, standing in front of the once-luxurious Beau Rivage casino, said at least a dozen gaming places were closed and damaged from Katrina -- costing the state $500,000 a day in lost tax revenues.
Charles Curtis, a Biloxi resident who works in a casino that is now split in half, said he and his wife stood on top of their refrigerator as the water rose around them.
"The Back Bay of Biloxi came through our front door," he said, referring to the shallow, marshy strip that borders the north of the city.
"We were ready to punch a hole through the ceiling if we had to" escape, Curtis said.
In Mobile, Alabama, the storm pushed water from Mobile Bay into downtown, submerging large sections of the city, and officials imposed a dusk-to-dawn curfew.
An oil drilling platform broke away from its moorings and lodged under a bridge that carries U.S. Highway 98 over the Mobile River.
The Alabama National Guard activated 450 troops to secure Mobile. Two other Alabama battalions, or about 800 troops, were activated to assist in Mississippi.
President Bush was returning to Washington two days ahead of schedule to help oversee Hurricane Katrina recovery efforts, the White House announced. (Full story)
The Federal Emergency Management Agency is preparing to house "at least tens of thousands of victims ... for literally months on end," the agency's director, Michael Brown, said Monday night.
Veteran FEMA staffers who have surveyed the destruction are reporting some of the worst damage they have ever seen, he said. (Full story)
Louisiana and Mississippi officials urged evacuees as well as those stranded by flooding from the storm to stay put.
"It's too dangerous to come home," said Blanco, who ordered state police to block re-entry routes to all but emergency workers.
The American Red Cross said it is launching the largest relief operation in its history.
More than 75,000 people are being housed in nearly 240 shelters across the region, and Red Cross President Marty Evans told CNN, "We expect that to grow" as people who can't return home seek somewhere to stay.
More than 1.7 million homes and businesses in Louisiana, Mississippi, Alabama and Florida were without electricity, according to utility companies serving the region.
Katrina was downgraded to a tropical depression Tuesday. As of the 11 a.m. ET update from the National Hurricane Center, Katrina was about 25 miles south of Clarksville, Tennessee, moving north-northeast at 21 mph.