New Orleans was filling with water after an initial attempt to stop a leaking levee failed, while police fought a losing battle to stop widespread looting in the stricken city.

In Mississippi, officials confirmed that at least 100 people had died in the killer storm and said the death toll was almost certain to go much higher.

"We're just estimating, but the number could go double or triple from what we're talking about now," a civil defense director told the Jackson, Mississippi Clarion Ledger.

Biloxi, Mississippi spokesman Vincent Creel earlier told Reuters of the death toll: "It's going to be in the hundreds."

US Sen. Mary Landrieu told reporters she had heard at least 50 to 100 people were dead in New Orleans, where rescue teams were so busy saving people stranded in flooded homes they had to leave bodies floating in the high waters.

Louisiana officials said 3,000 people had been rescued, but many more were waiting to be picked up by rescuers in boats who cruised up and down flooded streets or helicopters buzzing overhead.

"I'm alive. I'm alive," shouted one joyous woman as she was ferried from a home nearly swallowed by the rising waters.

Katrina struck Louisiana on Monday with 140 mile per hour winds, while slamming into the coasts of neighboring Mississippi, Alabama and western Florida.

A 30-foot (10-meter) storm surge in Mississippi wiped away 90 percent of the buildings along the coast at Biloxi and Gulfport, leaving a scene of destruction that Mississippi Gov. Haley Barbour said was "like there'd been a nuclear weapon set off."

New Orleans at first appeared to have received a glancing blow from the storm, but the raging waters of Lake Pontchartrain tore holes in the levee system that protects the low-lying city, then slowly filled it up.

Mayor Ray Nagin said 80 percent of the city, much of it below sea level, was covered with water that was in places 20 feet deep.

The US Army Corps of Engineers and local levee workers tried, but failed on Tuesday to stem the flow from a 60 meter long breach near the city center with 1,360 kg sandbags brought in by helicopter.

Corps senior project engineer Al Naomi said they would bring in more sandbags on Wednesday and perhaps build a temporary dam around the breach.

But the biggest ally in the fight to save the city may be nature itself, he said.