Louisiana state officials prepared to abandon New Orleans to its fate today as the floodwaters engulfing the city carried on rising despite attempts by United States Army engineers to plug breached storm defences.

As the confirmed death toll from Hurricane Katrina climbed into triple figures, the Louisiana Governor said that the situation in New Orleans was becoming increasingly desperate.

President Bush, who broke off from a holiday at his ranch in Texas, is to host emergency talks on what looks set to be the country's most costly national disaster.

US government officials have declared a public health emergency for the entire Gulf Coast, calling life in the aftermath of Hurricane Katrina "very dangerous".

"The situation in all affected areas remains very dangerous," said Michael Chertoff, the secretary of homeland security.

The Health and Human Services Secretary, Michael Leavitt, said his agency is concerned about potential disease outbreaks and was sending medical experts from the Centers for Disease Control and Prevention. He urged residents of the coast area to boil water and follow food safety precautions, and avoid situations that might lead to carbon monoxide poisoning from electricity generators.

New Orleans appeared at first to have been spared the worse from Katrina, America's deadliest storm in more than 30 years, as the category four hurricane hit the Gulf Coast on Monday morning. But the floods brought by the storm breached the levees that protect the city - which lies mostly under sea level - and the New Orleans basin has been gradually filling up with water like a bathtub.

As the waters rise, the city has descended into lawlessness. Looters raided pharmacies and gun stores and gangs of armed men roamed the city. Staff and patients at the city's Children's Hospital, waited in vain for help as looters tried to break through the doors of the building.

The storm wrought devastation along the Gulf Coast, with one Mississippi county reporting at least 100 deaths - and possibly many more - and a neighbouring county at least ten. Thirty of the dead in Harrison County were from a beachfront apartment building that collapsed under a wall of water as Katrina hit the coast with 145mph winds.

Looters were busy across the coastal strip. In Biloxi, the town that suffered most from the storm, people picked through casino slot machines for coins and ransacked businesses - sometimes in full view of police and National Guardsmen.

In New Orleans, rescue workers have not even begun collecting, let alone counting, the bodies floating in the muddy torrents that have submerged 80 per cent of the city, in some places up to six metres (20ft) deep.

Last night Mayor Ray Nagin said that rescue boats were passing them by. "We’re not even dealing with dead bodies," Mr Nagin said. "They’re just pushing them on the side."

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