NEW ORLEANS is to be abandoned as flood waters pour in through huge breaches in the city’s defences. The Governor of Louisiana gave the order as the mayor said that thousands may have died.

“Minimum, hundreds. Most likely, thousands,” said Ray Nagin, the Mayor, when asked about the death toll. “There are dead bodies floating in the water. The rescuers were basically pushing them aside as they rescued people.”

The governor’s order has few precedents in modern history, but officials said that the city of 500,000 faced catastrophic destruction and could be rendered uninhabitable for months. President Bush said that it could take years to recover from the flooding.

“The devastation is greater than our worst fears,” said Kathleen Blanco, the state Governor, as she ordered the removal of the estimated 50,000 residents still left. “It is just totally overwhelming.”

In a dramatic move last night Mr Nagin ordered 1,500 police to suspend their rescue efforts and return to the streets to stop the widespread looting. An additional 10,000 National Guard troops have been sent into the stricken region, nearly doubling the total troop deployment, to help enforce law and order.

The Foreign Office said that no British citizens had died in the devastation. However, the fallout will reach Britain in the form of soaring petrol prices. They could top £1 a litre as US oil companies driveup demand by seeking alternative supplies from European refineries.

About 20 Britons were stuck with 20,000 other refugees in the New Orleans Superdome, which the authorities began to evacuate last night. A fleet of prison buses arrived to take the refugees to the Houston Astrodome 300 miles away.

Mr Bush was speaking after returning early to the White House from his Texas vacation to oversee recovery efforts. “We are dealing with one of the worst natural disasters in our nation’s history,” he said. “This recovery will take a long time. This recovery will take years.”

As the Pentagon rushed five Navy ships and eight maritime rescue teams to the region, armed looters ran amok. Three people were shot. “The looting is out of control,” said Jackie Clarkson, a council member.

Those left behind were running out of supplies, but rescue workers attempting to pluck people from rooftops were hampered by surging water filled with bodies, cars, concrete, alligators and poisonous snakes.

Gas leaks fuelled fires, authorities said that electricity would be out for weeks and two hospitals with more than 1,000 patients were abandoned.

“It’s like being in a Third World country,” said Mitch Handrich, a nurse at Charity Hospital where staff were ventilating patients by hand.

Terry Ebbert, the city’s homeland security chief, said that if the water levels rose several more feet the entire water system of New Orleans could be wiped out. Major-General Don Riley, of the US Army Corps of Engineers, said that it could take a month to get the water out of the city.

Sidney Barthelemy, the former Mayor, said that efforts to plug the breached levees were failing. “They’re losing hope,” he said.

Mr Nagin said that it would be 12 to 16 weeks before people could return.

He expressed frustration at the military’s failure to block a 300-foot breach near the 17th Street Canal, which was allowing water from Lake Pontchartrain to flood in. Despite dropping 3,000lb sandbags from helicopters, the flow of water seemed unabated.

Further along the Gulf Coast, the death and destruction were equally great. “We are looking now at a disaster above any magnitude that we’ve seen in the United States,” said Peter Teahen, a Red Cross spokesman.

The US Government declared a public health emergency for the entire Gulf Coast. “We are gravely concerned about the potential for cholera, typhoid and dehydrating diseases that could come as a result of the stagnant water and the conditions,” said Michael Leavitt, the US Health Secretary.

A 30-foot sea surge in Mississippi obliterated 90 per cent of buildings on the coast east of New Orleans. The town of Gulfport was virtually gone, as was much of Biloxi. More than 2.3 million homes were without electricity, including 80 per cent of Mississippi.

Samuel Bodman, the US Energy Secretary, announced that oil would be released from the emergency fuel reserve to help refiners. The US coast guard reported that at least 20 oil rigs and platforms were missing.

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