In New Orleans, shell-shocked officials tried to regain control of the historic jazz city reduced to a swampy ruin by Monday's storm. Bodies floated in the flooded city and authorities still could only guess how many people had died.
"We don't have numbers. It could be in the hundreds, or the thousands, "US Sen. Mary Landrieu of Louisiana said of the statewide death toll. "I think it's going to be shocking."
A National Guard official said as many as 60,000 people had gathered at the Superdome stadium for evacuation. But the evacuation was suspended when someone fired at a military helicopter sent to ferry out survivors.
New Orleans Mayor Ray Nagin ordered police to drop rescue operations to fight looting and other crime that gripped the city. A National Guard soldier was shot and wounded on Wednesday in the Superdome arena housing thousands of refugees in increasingly squalid conditions.
TROOPS ON THE WAY
Nearly 5,000 Louisiana National Guard troops were called to duty and 7,500 more were en route from other states, to be joined by state police from all over the nation, the National Guard said.
An angry Louisiana Gov. Kathleen Blanco told reporters: "We will do what it takes to bring law and order to our area."
"I'm just furious. It's intolerable," she said.
Louisiana wildlife officers said their boat crews were still rescuing 650 people an hour from the flooded city. Thousands waited hours or waded through floodwaters to catch rides out of New Orleans.
Storm survivors in the Superdome began clambering onto 300 buses that were shipping them 350 miles (560 km) west to another stadium, the Astrodome in Houston.
The first refugees began arriving early on Thursday at the Houston stadium, where Red Cross workers set out thousands of cots and "comfort kits" that included toiletries and a meal.
But the operation was put on hold when shots were fired at the helicopter, said a local official in Texas involved in the evacuation.
Trash fires near the Superdome and other logistic problems were also delaying the evacuation.
FIRES AND GUNSHOTS
Elsewhere in New Orleans, gunshots repeatedly rang out and fires flared as looters broke into stores, houses, hospitals and office buildings -- some in search of food, others looking for anything of value.
Similar scenes played out in Mississippi, where looters freely ransacked stores in Biloxi and Gulfport, both shattered by the storm that slammed into the Gulf Coast on Monday with 140 mile per hour (225 kph) winds and a 30-foot (9-metre) storm surge.
Mississippi Gov. Haley Barbour told NBC's "Today" show that part of the looting problem has been an inability to get enforcement personnel into critical areas. "We will have several thousand National Guard by the weekend and will put a stop to it," he said.
US President George W. Bush condemned the looting and warned against charging artificially high prices for gasoline.
"I think there ought to be zero tolerance of people breaking the law during an emergency such as this, whether it be looting, or price-gouging at the gasoline pump or taking advantage of charitable giving, or insurance fraud," Bush said in an interview on ABC's "Good Morning America."
The president said on Wednesday it could take years to recover from the devastation and the New Orleans mayor estimated it would be three to four months before residents could return. A million people fled the New Orleans area before Katrina arrived.
The US Army Corps of Engineers said floodwaters started to drop in New Orleans, which is mostly below sea level and was deluged by water from Lake Pontchartrain after levees broke.
"Water is now flowing slowly out of New Orleans because water is seeking its own level -- that of Lake Pontchartrain," the Corps said in a news release.
That would still leave most of the city under about 8 feet (2.4 metres) of water. The corps said it would it would open holes in parts of the city's levee system to let water drain out while at the same time attempting to fix several large breaches torn out by Katrina's storm surge.
Officials estimated it could take a month to get the water out.
NO WAY OUT
Some people left homeless in Mississippi and Louisiana were frustrated with relief efforts.
"Many people didn't have the financial means to get out," said Alan LeBreton, 41, an apartment superintendent who lived on Biloxi, Mississippi's seaside road, now in ruins. "That's a crime and people are angry about it."
The Biloxi Sun Herald newspaper said in an editorial emergency supplies "simply are not getting here fast enough" and asked "why hasn't every able-bodied member of the armed forces in South Mississippi been pressed into service?"
The Bush administration declared a public health emergency on Wednesday amid concern about outbreaks of disease and began working with Congress on emergency legislation to assist recovery efforts from the disaster that some officials said rivaled the Sept. 11, 2001, attacks.
The storm was having a national impact as gasoline prices soared.US gasoline futures shot up 15.47 cents to $2.41 a gallon, for October delivery, on the New York Stock Exchange as several refineries on theUS Gulf Coast remained shut.
The hurricane cut a swath through a region responsible for about a quarter of the nation's oil and gas output. The Bush administration said it would release oil from the nation's strategic reserves to offset the losses.
(Additional reporting by Mark Babineck in Baton Rouge, Louisiana, Paul Simao in Mobile, Alabama, Peter Cooney in Houston and Steve Holland in Washington)