Death and destruction ravaged the severely storm-battered Gulf Coast Tuesday, with as many as 80 dead in one Mississippi county alone as the frantic search for survivors of Hurricane Katrina (search) continued.

"We have nowhere to go," one broken man whose wife and house were swept away by floodwaters in Gulfport, Miss., told FOX News. "I lost everything. That's all I had. That's all I had."

Click here to track Tropical Depression Katrina.

Mississippi Gov. Haley Barbour (search) said there were unconfirmed reports of up to 80 deaths in Harrison County, which includes Gulfport and Biloxi, and the number was likely to rise. At least five other deaths across the Gulf Coast were blamed on Katrina.

"The devastation down there is just enormous," Barbour said on NBC's "Today" show, the morning after Katrina howled ashore with winds of 145 mph and engulfed thousands of homes in one of the most punishing storms on record in the United States.

The death toll does not include 11 deaths in South Florida when a much-weaker Katrina first hit land last week. The biggest known cluster of deaths was at the Quiet Water Beach apartments in Biloxi, where about 30 people died.

"This is our tsunami," Biloxi Mayor A.J. Holloway told the Biloxi Sun Herald.

And the death toll is expected to climb.

"I talked with paramedics that are on the scene and the devastation is so great that they won't quit counting (bodies) for a while," said Mark Williams, operations supervisor for American Medicial Response, which operated ambulances along the Mississippi coast.

As of Monday night, more than 37,000 people were in American Red Cross shelters along the Gulf Coast. Officials warned people against trying to return to their homes, saying that would only interfere with the rescue and recovery efforts.

Tens of thousands of people will need shelter for weeks if not months, said Mike Brown, director of the Federal Emergency Management Agency. And once the floodwaters go down, "it's going to be incredibly dangerous" because of structural damage to homes, diseases from animal carcasses and chemicals in homes, he said.

"We've got a floating cesspool right now," said Dr. Steven Garner, chief medical officer at St. Vincent Catholic Medical Center in New York City.

The Red Cross told reporters the Katrina relief effort would be bigger than that of Sept. 11.

"We know that there is a lot of the coast that we have not been able to get to," Barbour said. "I hate to say it, but it looks like it is a very bad disaster in terms of human life."

Floodwaters engulfed entire towns and cities, power was out, phone service was down and many were stranded. Thousands of National Guardsmen were activated in Louisiana, Mississippi, Alabama and Florida. Looting was breaking out in New Orleans and Biloxi.

President Bush is cutting short his vacation in Crawford, Texas, and will return to Washington on Wednesday instead of Friday to monitor the recovery effort.

"We have got a lot of work to do," Bush said Tuesday.

After striking the Gulf Coast as a Category 4 hurricane Monday, Katrina was soon downgraded to a tropical storm as it passed through eastern Mississippi, moving north at 21 mph.

By midday Tuesday, Katrina weakened to a tropical depression, with winds around 35 mph. Its remnants doused Tennessee with heavy rain and powered high winds that cut electricity to about 80,000 customers across the state on Tuesday. Katrina was at tropical force strength more than 320 miles north of the Gulf Coast when it entered Tennessee overnight.

Forecasters said that as the storm moves north over the next few days, it could swamp the Tennessee and Ohio valleys with a potentially ruinous 8 inches or more of rain.

Water Still Rising in New Orleans

In New Orleans, a city of 480,000, water began rising in the streets Tuesday morning after a 17th Street Canal floodwall was breached overnight. A second breach occurred on the Industrial Canal. The U.S. Army Corps of Engineers was dispatched to asses the situation.

"We're attempting to contract for materials, such as rock, super sand bags, cranes, etc., and also for modes of transportation — like barges and helicopters, to close the gap and stop the flow of water from Lake Pontchartrain into the city," said Walter Baumy, Engineering Division chief and project manager for closing the breach.

Officials said they were not 100 percent sure where else water was coming in but once the pumps began working and the leaks were plugged, it would take up to two weeks to get the water out of the city.

"It's a very slow rise, and it will remain so until we plug that breach. I think we can get it stabilized in a few hours," said Terry Ebbert, New Orleans' homeland security chief.

New Orleans lies mostly below sea level and is protected by a network of pumps, canals and levees. Many of the pumps were not working; about 80 percent of the city was under water.

A water main broke in New Orleans, making it unsafe to drink the city's water without first boiling it.

Water was knee-deep around the Superdome and was seeping into the French Quarter, which was nearly dry earlier in the morning. Canal Street was literally a canal. The Hyatt Hotel and other high-rise buildings around the Superdome had rows of shattered windows. The city considered bringing in barges to provide electricity. Officials requested that anyone with flat-bottomed boats volunteer them to aid in rescue efforts.

The mayor issued an emergency evacuation order and said schools would be closed for at least two months.

"At first light, the devastation is greater than our worst fears. It's just totally overwhelming," Louisiana Gov. Kathleen Blanco said.

Louisiana officials said people in some swamped neighborhoods were feared dead. The governor said only: "We have no counts whatsoever, but we know many lives have been lost."

Downtown streets that were relatively clear in the hours after the storm were filled with 1 to 1 1/2 feet of water Tuesday morning as pumps and levees failed.

The rising water forced one New Orleans hospital to move patients to the Louisiana Superdome, where some 10,000 people had taken shelter, and prompted the staff of New Orleans' Times-Picayune newspaper to abandon its offices.

National Guardsmen brought in people from outlying areas to the Superdome in the backs of 2 1/2-ton Army trucks. Louisiana's wildlife enforcement department also brought people in on the backs of their pickups. Some were wet, some were in wheelchairs, some were holding babies and nothing else.

'Total Devastation' in Mississippi

All along the Gulf Coast, tree trunks, downed power lines and trees, and chunks of broken concrete in the streets hampered rescue efforts, which were being conducted by boat and helicopter. Crews worked to clear highways. Along one Mississippi highway, motorists themselves used chainsaws to remove trees blocking the road.

Officials said it could be a week or more before many of the evacuees are allowed back.

"I don't want anyone not in the city to come back. What we're doing is trying to make the best of a bad situation and we need people to cooperate," New Orleans Police Chief Eddie Compass said.

The hurricane knocked out power to more than 1 million people from Louisiana to the Florida Panhandle; authorities said it could be two months before electricity is restored to everyone.

"We know that last night we had over 300 folks that we could confirm were on tops of roofs and waiting for our assistance. We pushed hard all throughout the night. We hoisted over 100 folks last night just in the Mississippi area. Our crews over New Orleans probably did twice that," Capt. Dave Callahan of the Coast Guard Aviation Training Center in Mississippi said in a television interview.

Teresa Kavanagh, 35, of Biloxi, shook her head is disbelief as she took photographs of the damage in her hometown.

"Total devastation. Apartment complexes are wiped clean. We're going to rebuild, but it's going to take long time. Houses that withstood Camille are nothing but slab now," she said. Hurricane Camille killed 256 people in Louisiana and Mississippi in 1969.

The storm's surge put at least five Mississippi casinos out of commission. The Hard Rock Cafe and Beau Rivage were severely damaged. The bottom floors of a condominium were all but washed away. All that remained of one hotel was the toilets.

Katrina's surge also demolished major bridges along the coast. The storm swept sailboats onto city streets in Gulfport and obliterated hundreds of waterfront homes, businesses, community landmarks and condominiums.

Anne Anderson said she lost her family home in Gulfport, Miss.

"My family's an old Mississippi family. I had antiques, 150 years old or more, they're all gone. We have just basically a slab," she told NBC. "Behind us we have a beautiful sunrise and sunset, and that is going to be what I'm going to miss the most, sitting on the porch watching those."

Oil prices jumped by more than $3 a barrel on Tuesday, climbing above $70 a barrel, amid uncertainty about the extent of the damage to the Gulf region's refineries and drilling platforms. Preliminary assessments said the insurance industry faces as much as $26 billion in claims from Katrina, making this storm more expensive than the previous record-setting storm, Hurricane Andrew (search), which caused some $21 billion in insured losses in 1992 to property in Florida and along the Gulf Coast.

FOX News' Catherine Donaldson-Evans, Phil Keating, Rick Leventhal, Caroline Shively, Shepard Smith, Dan Springer and The Associated Press contributed to this report.