There are reports of rotting corpses lining the city streets, and of survivors forced to scavenge for food and camp in streets littered with garbage and human faeces.
New Orleans mayor Ray Nagin has issued an urgent SOS for thousands of people stranded at the city’s convention centre, at the Louisiana Superdome and in attics across the city, many with no food or water.
Around 300 National Guardsmen have arrived in the city, ordered to restore civil order with a shoot-to-kill policy.
However it comes too late, with horrific reports of shootings, rapes and rioting inside the Louisiansa Superdome.
Kathleen Blanco, Louisiana’s governor, said “the whole region could evacuate 200,000, 300,000, maybe more,” as the extent of the catastrophe unfolded.
Around 80 percent of New Orleans remains under water days after two sections of the protective levees encircling the city ruptured.
About 15,000 to 20,000 people who sought refuge in New Orleans Convention Centre recounted tales of horror as they waited for rescuers to arrive.
With authorities struggling to keep up with the crisis people have increasingly taken matters into their own hands, spawning a wave of lawlessness.
“As the night went on, people were dying off. There were people shooting, fights broke out, the bathrooms were clogged up and there was no water,” 28-year-old Keshia Gray said of conditions at the convention centre.
Some survivors said they had seen the bodies of people shot dead lying in front of the centre.
By morning, at least seven bodies reportedly lay scattered around the building, one old man lying dead on a chaise lounge on grass outside and another elderly woman in a wheelchair covered by a blanket.
“I don’t treat my dog like that,” 47-year-old Daniel Edwards told the Associated Press news service, pointing to the woman’s body.
“I buried my dog.”
“You can do everything for other countries, but you can’t do nothing for your own people. You can go overseas with the military, but you can’t get them down here,” Mr Edwards added, venting his frustration at the pace of the relief effort.
“They’ve been teasing us with buses for four days,” he added.
In the hope of defusing a potentially explosive situation, Mayor Nagin gave people permission to search out food and water in New Orleans’ few dry areas.
In a statement to CNN, he said: “This is a desperate SOS. Right now we are out of resources at the convention centre and don’t anticipate enough buses. We need buses. Currently the convention centre is unsanitary and unsafe and we’re running out of supplies.”
An equally fraught situation has taken hold of New Orleans’ Superdome, where up to 25,000 people have been sheltering.
A line of heavily armed policemen and some of the 6,000 National Guards sent to the city kept watch over exhausted crowds clambering onto buses destined to take them 560 kilometres to Houston’s Astrodome in Texas.
Around 11,000 people are now sheltering at the Astrodome and officials said it has reached capacity and will take no more people.
Refugees are being taken to other shelters.
An ambulance service in charge of airlifting the sick and injured from the sports arena suspended its flights after a helicopter reportedly came under gun fire.
At New Orleans hospitals, attempts to evacuate patients have been similarly thwarted.
“Hospitals are trying to evacuate,” said Coast Guard Lieutenant Commander Cheri Ben-Iesan, a spokesman at the city emergency operations centre.
“At every one of them, there are reports that as the helicopters come in, people are shooting at them. There are people just taking pot shots at police and at helicopters, telling them, ‘You better come get my family’.”
Police Captain Ernie Demmo said at least one National Guard military policeman had been injured, taking a gunshot wound in the leg after a man tried to grab the officer’s rifle.
Rescue efforts have been put on hold as resources have been diverted to stamp out the rampant looting and violence and Governor Blanco said she had called for 40,000 uniformed troops.
Asked how long people still trapped on roofs and in attics could hold out, Ms Blanco said “some are sturdy, but some are on a very short time line.”
Mayor Nagin has also ordered most of the city’s police to concentrate on restoring order, and US President George W Bush has called for ‘zero tolerance’ on armed gangs and profiteers.
But the longer people stay in New Orleans, the greater the risk of an outbreak of water-born disease spreading from the sewage and rubbish tainted floodwaters.
As anger and frustration mount, US Homeland Security Secretary Michael Chertoff defended the government’s response to the disaster which stretches across 234,000 square kilometres and four states.
“We’re not only confronting the original disaster, the hurricane, we’re confronting the ongoing disaster, the flood,” Mr Chertoff explained.
“For those who wonder why it is difficult to get these supply and medical teams into place, the answer is, they are battling an ongoing dynamic problem with the water.”
In Washington, President Bush attempted to reassure victims that help was at hand.
“I understand the anxiety of people on the ground… So there is frustration. But I want people to know there’s a lot of help coming,” Mr Bush said.
The president and Congress have returned early from their summer recess to expedite a bill that will release US$10 billion in aid.
Once Mr Bush signs off on the bill, he will head south for a comprehensive tour of the devastated Gulf States on Friday.