Hurricane Katrina smashed into New Orleans this morning, disrupting power and submerging part of the low-lying city in up to 6ft of water.
Downtown New Orleans today
At least 10,000 people sought refuge in the city's 77,000-seat Superdome, which had part of its roof ripped off by winds of more than 140mph.
The storm changed course slightly as it hit land, downgrading from Category 5 - the strongest - to a powerful Category 3, sparing the vulnerable city from the worst case scenario despite wreaking havoc across four states.
Winds sent debris flying through the New Orleans' streets, blew windows out of high-rise hotels and tore through the roof of the Superdome.
Gov. Kathleen Blanco said the damage had caused leaks and evacuees had been moved to dry areas in the stadium, but there was no immediate danger.
By 6 p.m. Irish time, Katrina's winds had decreased to 105 mph, a Category 2 storm, with its centre moving ashore at the Louisiana-Mississippi border.
New Orlean's levee system appeared to be holding off the Mississippi River and Lake Pontchartrain on its edges. Officials said a breach occurred in nearby St. Bernard Parish, where Katrina's eye passed and extensive damage was expected.
About 150 people were reported stranded on rooftops in a southeastern Louisiana parish, where officials 2.5 to 3 meters of water swamped the region.
"We're getting reports that (more than 20) buildings are collapsing throughout the city," New Orleans Mayor Ray Nagin said, adding it remained unsafe at midday. "This city is under siege by Katrina."
However, Katrina's slight eastern turn that might have saved New Orleans brought its powerful winds and tides into Mississippi coastal tourist havens of Biloxi and Gulfport.
The National Hurricane Centre said the exposed Mississippi coastline could expect 4.5 to 6-metre storm surges. Mobile Bay in Alabama was swelling on Katrina's approach.
Weather experts had predicted thousands of homes could be damaged or destroyed and a million people left homeless if the storm surge is too great for the levees to hold back.
Officials estimated a million people had left the area ahead of the storm, which was once a fearsome Category 5 with winds of 175 mph, but many chose to ride it out. It hit land as a Category 4 on the five-step Saffir-Simpson scale.
Meanwhile, President George W. Bush approved "major disaster declarations" for the states of Louisiana and Mississippi.
"This will allow federal funds to start being used to deploy resources to help in those two states," White House spokesman Scott McClellan told reporters travelling with Bush to Arizona. He said the money would be used for "response and recovery" efforts.
Agencies