New Orleans Mayor Ray Nagin has issued an urgent plea for relief, saying the city lacked food for thousands of Hurricane Katrina's refugees and buses to evacuate them.
Mr Nagin said the Convention Center is now unsanitary and unsafe and they are running out of supplies for the 15,000 to 25,000 people there.
And Louisiana Governor Kathleen Blanco said she had asked for 40,000 uniformed troops to restore order in New Orleans.
The US President, George W Bush, earlier said looters plundering shops should be treated with 'zero tolerance'.
His comments came as the operation to evacuate the remaining residents from New Orleans was delayed after shots were fired at a rescue helicopter by people on the ground.
A local spokesman also said gunmen shot and wounded a National Guardsman outside the Superdome stadium in the city.
Amid fears that law and order is breaking down, hundreds of police have been taken off search-and-rescue duties in the flooded city to counter looters who seized control of the streets, raided shops and held up car drivers at gunpoint.
Television pictures showed hundreds of stranded people have gathered on the streets near the city's convention centre, apparently still awaiting emergency assistance.
There is no exact figure of the number of people left in the city, but it is thought it could be between 50,000 and 100,000.
Coaches had been taking people to the state capital of Louisiana, Baton Rouge, as well as the neighbouring state of Texas.
Most of New Orleans remains submerged, and there is growing concern about the threat from water-borne diseases.
The death toll in the US Gulf States is not known, but New Orlean's mayor Ray Nagin warned that in New Orleans alone it could be in the thousands. He further warned that the clean-up operation could take up to four months.
The Department of Foreign Affairs said it is attempting to contact Irish citizens known to have been in New Orleans or the surrounding area which has been affected by Hurricane Katrina.
The families of up to ten Irish people have contacted the Department requesting help in tracking down their relatives.
Medical shelters
As relief efforts continue, medical and relief supplies are on their way to Mississippi and Louisiana. Medical shelters are being set up offering 10,000 beds, while the US military is providing dozens of rescue helicopters and boats.
The Pentagon has ordered 10,000 extra national guardsmen to be despatched to Louisiana and Mississippi. This will bring to 21,000 the total number of troops in areas hit by the hurricane.
Speaking last night as he launched the federal government effort to relieve the situation, President Bush said it would take years to recover.
Mr Bush viewed the devastation in Louisiana, Mississippi and Alabama on a flight back to Washington from Texas. Speaking at the White House, he described the storm as one of the worst natural disasters in the nation's history.
Mr Bush's political opponents have accused him of taking too long to respond, while there is concern that troop numbers are overstretched because of commitments in Iraq.
