A widespread disaster unfolded on the US Gulf Coast on Tuesday as up to 80 people were reported dead in Mississippi, and floodwaters poured into low-lying New Orleans through levees battered by powerful Hurricane Katrina.
Mississippi Gov. Haley Barbour told the NBC "Today" show there were reports of 50 to 80 fatalities in one coastal county alone, Harrison County.
"They are unconfirmed but likely are accurate and likelier to go up when we take in the other counties," Barbour said.
Local media said 30 people died at a Biloxi apartment complex where they were drowned or crushed by debris, and New Orleans' mayor reported bodies floating in floodwaters.
The death toll was expected to grow as rescuers struggled through high water and mountains of debris to reach areas devastated by Katrina when it struck the region on Monday. Hundreds needed to be rescued from rooftops, US Coast Guard officials said.
The storm inflicted catastrophic damage all along the coast as it slammed into Louisiana with 140 mph (224 kph) winds, then swept across Mississippi, Alabama and Tennessee.
It shattered buildings, broken boats, smashed cars, toppled trees and flooded cities. Risk analysts estimated the storm would cost insurers $26 billion, the most in US history.
Most of the deaths appear to have been caused by a massive storm surge that swept in from the sea and as far as a mile (1.5 km) inland in parts of Mississippi.
"The state has suffered a grievous blow on the coast," Barbour told reporters.
No deaths have been officially confirmed in Louisiana, but New Orleans Mayor Ray Nagin said bodies were floating in high waters that covered most of the city.
"The city of New Orleans is in a state of devastation," he told television station WWL. We probably have 80 percent of our city under water; with some sections of our city the water is as deep as 20 feet (6 metres). We still have many of our residents on roofs," he said. "Both airports are under water."
New Orleans is mostly below sea level and protected by levees or embankments.
Nagin said the levees had given way in places to Katrina's storm surge, including a 200-foot (60 metre) breach near the city center through which waters from Lake Pontchartrain were pouring in.
"There's a serious leak and it's causing the water to continue to rise," he said. Adding to the problem were malfunctions in the system the city uses to pump out floodwaters.
So far, Nagin said, the historic French Quarter and central business district had not been badly flooded.
But Tulane University Medical Center vice president Karen Troyer-Caraway told CNN the downtown hospital was surrounded by 6 feet (two metres) of water and considering evacuating its 1,000 patients.
"The water is rising so fast I cannot begin to describe how quickly it's rising," she said. "We have whitecaps on Canal Street, the water is moving so fast."
Louisiana emergency-preparedness officials said plans were in the works to fix the broken levee.
The high waters flooded thousands of homes and forced many people into attics and onto roofs.
Police took boats into flood-stricken areas to rescue some of the stranded. Others were picked up by helicopter.
People used axes, and in at least one case a shotgun, to blast holes in roofs so they could escape their attics. Many who had not yet been rescued could be heard screaming for help, police said.
"This is a horror story. I'd rather be reading it somewhere else than living it," said Aaron Broussard, president of New Orleans' Jefferson Parish.
In Mississippi, water swamped the emergency operations center at Hancock County courthouse and the back of the building collapsed.
"Thirty-five people swam out of their emergency operations center with life jackets on," neighboring Harrison County emergency medical services director Christopher Cirillo told Mississippi's Sun Herald newspaper. "We haven't heard from them."
The storm revived memories of Hurricane Camille, which hit the region in 1969 with winds up to 200 mph (320 kph) and killed 256 people.
Before striking the Gulf coast, Katrina last week hit southern Florida, where it killed seven people.
Katrina knocked out electricity to about 2.3 million customers, or nearly 5 million people, in Louisiana, Mississippi, Alabama and Florida, utility companies said. Restoring power could take weeks, they warned.
On its way to the coast, the storm swept through oil and gas fields in the Gulf of Mexico where 20 percent of the nation's energy is produced.
At least two drilling rigs were knocked adrift and one in Mobile Bay, Alabama, broke free of its mooring and slammed into a bridge.
US oil prices on Monday jumped nearly $5 a barrel in opening trade to peak over $70 and on Tuesday was holding above $68 as oil firms assessed damage.
Governors in Louisiana, Mississippi, Alabama and Florida had summoned a total of at least 7,503 Army and Air Force National Guard troops to state duty to provide services ranging from law enforcement to debris removal and providing portable generators for electric power, Pentagon spokesman Bryan Whitman said.
By Tuesday morning, Katrina had moved inland to north-eastern Mississippi where the National Hurricane Center in Miami said it was downgraded to a tropical storm with 50 mph (80 kph) winds.