Rescuers worked through the night to reach hundreds of people stranded after Hurricane Katrina ripped across the Gulf Coast killing dozens of people, destroying countless homes and leaving more than a million people without power in three states.
And authorities said they would not be able to reach some of the hardest-hit areas until first light on Tuesday.
The storm is blamed for at least 68 deaths and that toll is almost certain to rise. Mississippi officials said at least 55 people were killed there, including 30 who were killed in an apartment complex near the Biloxi beach. Alabama reported two deaths. The storm killed 11 people last week when it made its initial landfall in Florida.
While Louisiana officials have not yet confirmed any deaths there, New Orleans Mayor Ray Nagin said there have been reports of bodies floating in the floodwaters.
In Mississippi, streets and homes were flooded as far as six miles inland, and the eastbound lanes of Interstate 10 between Gulfport and Biloxi were impassible because of debris deposited in the roadway by floodwaters.
"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.
A 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 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."
Hotel worker Suzanne Rodgers returned to her beachfront home near Biloxi, but, she told CNN, "there is nothing there. There's debris hanging from trees."
"All I found that belonged to me was a shoe," she said. "There's nothing left."
At least 30 people were killed at the St. Charles apartment complex, near the beach in the casino resort town of Biloxi, said Kelly Jakubic with the county's Emergency Operations Center.
Separately, the Mississippi Emergency Management Agency in Jackson confirmed five Katrina-related deaths, a spokeswoman said.
Two people lost their lives in storm-related traffic accidents in Alabama.
Water poured into New Orleans 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.
"My heart is heavy tonight," Nagin said in the interview on CNN affiliate WWL-TV. "I don't have any good news to share."
In the city's 9th Ward neighborhood, rescue efforts continued throughout the night, with authorities in boats plucking residents from submerged homes after water topped another levee.
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.
Louisiana Gov. Kathleen Blanco told CNN Monday that a 50-inch water main was severed during the storm, cutting the supply of drinkable water.
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.
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.
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 1.3 million homes and businesses in Louisiana, Mississippi and Alabama were without electricity, according to utility companies serving the region.
As of 5 a.m. ET Tuesday, Katrina was about 35 miles northeast of Tupelo, Mississippi, according to the National Hurricane Center. The center's next update will be at 11 a.m.
The storm was headed north Monday night through Mississippi toward Tennessee and the Ohio River Valley. But even as a tropical storm, Katrina was still causing plenty of trouble.