President George Bush has conceded the initial response to Hurricane Katrina was "not acceptable" but has said every effort is being made to save lives.
President Bush has promised to help rebuild the devastated areas
Heavily-armed National Guardsmen have begun pouring into New Orleans, where thousands remain stranded without food or water amid rising lawlessness.
A large military convoy carrying aid also entered the city on Friday.
Visiting the region, Mr Bush said order would be restored and New Orleans would emerge from its "darkest days".
"My attitude is, if it's not going exactly right, we're going to make it go exactly right. If there's problems, then we'll address the problems," Mr Bush said.
"Every life is precious and so we are going to spend a lot of time saving lives, whether it be in New Orleans or on the coast of Mississippi. We have a responsibility to help clean up this mess."
Speaking in Mobile, Alabama, Mr Bush said a $10.5bn (£5.7bn) emergency aid approved by the Senate was "just a small down-payment" on the cost of helping people rebuild.
He went on to visit Biloxi, on the Mississippi coast, where he comforted a woman who wept as she described how she had lost everything.
Four days after the hurricane struck, the scale of the casualties is still not known.
However one senator from Louisiana, David Vitter, has predicted the death toll could climb above 10,000 in Louisiana alone.
Thousands of extra troops have begun pouring into New Orleans
Senator Vitter said he did not base his estimate on any official toll.
The head of the New Orleans emergency operations has described the relief effort as a national disgrace.
And Mayor Ray Nagin has angrily denounced the level of outside help the city has received. "People are dying here," he said.
Army engineers have said it will take anything from 36 to 80 days to pump the flood waters from the city.
Meanwhile airlines have begun providing relief flights, bringing in supplies and flying out with people from New Orleans' Louis Armstrong International Airport at a rate of four an hour.
Most of the flights will take refugees to Texas, which is providing emergency shelter for 75,000 survivors in Houston, Dallas and San Antonio.
'Shoot to kill'
Clouds of acrid, black smoke have been drifting over New Orleans following a series of huge blasts along the Mississippi riverfront, apparently at a chemical plant.
The incidents in the already crippled city came after Louisiana's governor said 300 "battle-tested" National Guardsmen were being sent to quell the unrest.
"They have M-16s and are locked and loaded. These troops know how to shoot and kill and I expect they will," Kathleen Blanco said.
Washington pledged a further 4,200 guardsmen in coming days and said 3,000 army soldiers may also be sent to the city, where violence has disrupted relief efforts.
The deployment came as thousands were finally taken from the Louisiana Superdome, where up to 20,000 have been corralled amid heat and squalor since Katrina struck.
Heavily-armed soldiers flanked a large convoy of National Guard trucks as it arrived at the nearby convention centre with desperately needed supplies of food and water.
The BBC's Matt Frei, in New Orleans, says conditions in the convention centre, where up to 20,000 people are stranded, are the most wretched he has seen anywhere, including crises in the Third World.
"You've got an entire nursing home evacuated five days ago - people in wheelchairs sitting there and slowly dying," he says.
The situation has been made worse by a lack of trust between the mainly poor, African-American population left behind in New Orleans and the predominately white police force, our correspondent adds.
Up to 60,000 people could still be stranded in the city, the US coastguard says.
Looting has swept the city as people made homeless by the flooding have grown increasingly desperate.
There have also been outbreaks of shootings and carjackings and reports of rapes.
The federal emergency agency was trying to work "under conditions of urban warfare", director Michael Brown said.
The muddy floodwaters are now toxic with fuel, battery acid, rubbish and raw sewage.
According to the White House, about 90,000 sq miles (234,000 sq km) have been affected by the hurricane.