An estimated 80 per cent of the historic US city of New Orleans is under water after the city's defences were breached by the force of hurricane Katrina.
With floodwaters from the nearby Lake Ponchartrain rising in many areas, threatening the French Quarter, residents were plucked from the roofs of their homes, bodies were seen floating in the streets and rescuers searched the city in boats and helicopters.
"We probably have 80 percent of our city under water; with some sections of our city the water is as deep as 20 feet. Both airports are underwater," Mayor Ray Nagin told a radio interviewer.
New Orleans, a city that usually throbs with the life of its carnivals and the sound of jazz and blues, was in a "state of devastation," Nagin said.
In many residential areas TV pictures showed the water was up to roof level after the surge caused by Katrina breached a section of the levee along a canal leading from Lake Ponchartrain, which looms to the north of the city.
Much of New Orleans, a city of some 500,000, lies below sea level, bounded by the lake and the Mississippi River, North America's biggest river, which curves along the south of the city before discharging in the Gulf of Mexico.
"We always were afraid the bowl that is New Orleans would fill quickly," Walter Maestri, emergency management coordinator for Jefferson Parish, said in a radio interview. "Now with the water rising today, it appears to be filling slowly," he said.
"The water is rising so fast I cannot begin to describe how quickly it's rising," Tulane University Medical Center Vice President Karen Troyer-Caraway told CNN. "We have whitecaps on Canal Street, the water is moving so fast."
The downtown hospital was surrounded by 6 feet of water and considering evacuating its 1,000 patients.
"The devastation is greater than our worst fears," Louisiana Gov. Kathleen Blanco said in a news conference. "It's totally overwhelming."
Weather experts had predicted the city would be quickly overwhelmed by the impact of Katrina, which tore across the coast on Monday but initially damage appeared less than catastrophic.
Fears are gowing about pollution, with the water believed to be carrying sewage, spilled fuel and other pollutants from residential and commercial districts inundated in the flood.
Reporters said there was waist-high water round the Superdome, the huge covered football stadium near downtown New Orleans that had been used as an emergency evacuation center for thousands of residents.
Local television showed people and dogs sitting on rooftops, the houses below them invisible in brackish water. A hand was visible through a window in a house surrounded by chest-high water.
One man was seen using an ice chest as a flotation device. Another clung to metal scaffolding to escape the deluge, which ironically occurred in sunshine and blue skies Tuesday.
Officials went on television to urge people not to try to return to their homes yet. "You need to get used to where you're at right now because this may take us some time." said US Rep. Bobby Jindal.