GULFPORT, Miss. (AP) - As dawn broke over the ravaged Gulf Coast on Tuesday, rescuers in boats and helicopters furiously searched for survivors of Hurricane Katrina. The governor said the death toll in just one Mississippi county could be as high as 80.

''The devastation down there is just enormous,'' Gov. Haley Barbour said Tuesday on NBC's ''Today'' show.

Barbour said there were unconfirmed reports of up to 80 fatalities in Harrison County, which contains Gulfport and Biloxi, and the number was likely to rise.

''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.''

Tree trucks, downed power lines and chunks of broken concrete that littered streets hampered rescue efforts. Swirling water in many areas hid submerged dangers.

The official death toll jumped sharply late Monday when Harrison County emergency operations center spokesman Jim Pollard said an estimated 50 people had died in the county, with some 30 of the dead at a beach-side apartment complex in Biloxi.

Mississippi Emergency Management Agency officials refused to confirm the deaths. Three other people were killed by falling trees in Mississippi and two died in a traffic accident in Alabama, authorities said.

The total does not include 11 deaths in South Florida when a much-weaker Katrina first made landfall last week.

In New Orleans, residents who had ridden out the brunt of Katrina now faced a second more insidious threat as two different levee breaches sent a churning sea of water from Lake Pontchartrain coursing through city streets Tuesday.

Col. Rich Wagenaar of the Army Corps of Engineers, said a breach in the eastern part of the city was causing flooding and ''significant evacuations'' in Orleans and St. Bernard parishes. He did not know how many people were affected by the flooding.

Authorities said there was also a levee breach in the western part of the city. Jason Binet, of the Army Corps of Engineers, said that breach began Monday afternoon and may have grown overnight.

''The hurricane was scary,'' Scott Radish told The Times-Picayune. ''All the tree branches fell, but the building stood. I thought I was doing good. Then I noticed my Jeep was under water.''

Across the Gulf Coast, people were rescued as they clung to rooftops, hundreds of trees were uprooted and sailboats were flung about like toys when Katrina crashed ashore Monday in what could become the most expensive storm in U.S. history.

Katrina knocked out power to more than a million people from Louisiana to the Florida Panhandle, and authorities said it could be two months before electricity is restored to everyone. Katrina disrupted Gulf Coast petroleum output and rattled energy markets.

According to preliminary assessments by AIR Worldwide Corp., a risk modeling firm, the property and casualty insurance industry faces as much as $26 billion in claims from Katrina.

That would make Katrina more expensive than the previous record-setting storm, Hurricane Andrew, which caused some $21 billion in insured losses in 1992 to property in Florida and along the Gulf Coast.