Hurricane Katrina weakened slightly as it pummeled the Gulf Coast Monday, but the powerful storm still had plenty of punch as it swept through Mississippi with maximum sustained winds of 105 mph.
The weather service reported that "extensive and life-threatening storm surge flooding" was occurring along the Louisiana and Mississippi coast.
Mississippi Gov. Haley Barbour told reporters that Katrina "came in on Mississippi like a ton of bricks."
When asked what was his greatest fear, Barbour replied grimly "that there are a lot of dead people down there."
The storm passed just east of New Orleans, straining the system of levees and pumping stations that protect the low-lying city. About 70 percent of the city sits below sea level.
The National Weather Service reported that water had overtopped levees in Orleans and St. Bernard parishes.
The Lower 9th Ward, on the east side of New Orleans was under five to six feet of rising water after three pumps failed, according to WGNO reporter Susan Roesgen, who is with New Orleans Mayor Ray Nagin. She said New Orleans police had received more than 100 reports of people trapped on their roofs.
The Associated Press reported that entire neighborhoods along the south shore of Lake Pontchartrain were flooded, and residents had scrambled onto the roofs of their shotgun-style houses.
"I'm not doing too good right now," Chris Robinson told the AP via cell phone from his home east of the city's downtown. "The water's rising pretty fast. I got a hammer and an ax and a crowbar, but I'm holding off on breaking through the roof until the last minute. Tell someone to come get me please. I want to live."
CNN's John Zarrella reported wind howling through the streets and water "like waves on the ocean.
"Up through the manhole covers, water is pouring through the manhole covers," he said. "It can't take it."
Police and emergency workers should be able to enter the area and evaluate the situation by 2 p.m. (3 p.m. ET), according to Col. Terry Ebbert, director of homeland security for New Orleans.
"We'll have several hours of daylight to ... make an assessment and get out into those areas we're capable of getting into before the hours of darkness to take care of those people who are able to survive," Ebbert said.
Authorities in Gulfport, Mississippi, told CNN's Gary Tuchman that 10 feet of water covered downtown streets.
"Because the water is so deep, boats are floating up the street," Tuchman said. "There is extensive damage here. This is essentially right now like hell on earth."
"There is intense damage," he said. "We are watching the dismantling of a beautiful town."
CNN's Rob Marciano reported extensive damage in Biloxi, east of Gulfport. "Just a few minutes ago, the wind, surely over 100 mph, peeled roofs off, hurling 6-by-8 sheets of plywood into our parking lot, blowing out the windows of SUVs," he said.
Farther east, Mobile Bay spilled into downtown Mobile, Alabama, as the outer bands of the storm lashed the city.
A 20-foot storm surge is forecast as Katrina pushes inland.
At 2 p.m. ET, Katrina was centered about 20 miles southwest of Hattiesburg, Mississippi, the National Hurricane Center said.
The NHC said the storm had degraded to Category 2 status on the Safir-Simpson scale with maximum sustained winds near 105 mph. Hurricane force winds extended for 125 miles. Katrina came ashore Monday morning in southeastern Louisiana with winds topping 140 mph.
The National Weather Service said it had received many reports of "total structural failure" in the New Orleans metro area. It did not elaborate, but video from the city showed crumbled walls in one neighborhood.
About 10,000 people, who were unable to evacuate the city, took shelter in the Louisiana Superdome -- the cavernous football stadium that is usually home to the New Orleans Saints.
Reporter Ed Reams from affiliate WDSU told CNN that Katrina ripped away a large section of the building's roof.
"I can see daylight straight up from inside the Superdome," Reams reported. National Guard troops moved people to the other side of the dome. Others were moving beneath the concrete-reinforced terrace level.
Outside, CNN's Jeanne Meserve said that Teflon membrane that covers the top of the dome "has been shredded." "It's hanging off the top of the Superdome," she said.