Rescue crews pushed bodies aside to get to stranded victims of Hurricane Katrina as hundreds were feared dead in a humanitarian crisis that officials warned would intensify as flood waters rise further.

"The devastation is greater than our worst fears," said Louisiana State Governor Kathleen Blanco said. "It is just totally overwhelming."

Lake Pontchartrain was spilling slowly into the low-lying city of New Orleans after an effort to plug a breach in a levee failed Tuesday and pumps gave out. Looting broke out in some areas and gas leaks fueled fires.

"Over the next 12 to 15 hours, water will rise on the east bank of New Orleans to the levels where some sections of the city which are dry now could see nine or 10 feet (more than three meters) of water," Mayor Ray Nagin told CNN television late Tuesday.

Residents were advised to evacuate the Orleans and Jefferson neighborhoods on the east bank where water levels could rise significantly.

Rescuers in boats and helicopters struggled to reach hundreds of survivors stranded on rooftops, their efforts hampered by live power lines, broken gas pipes and debris including cars floating below the surface of the rising waters.

Governor Blanco said hundreds of people had been brought to dry ground, but warned to expect a grim toll: "We know that many lives have been lost."

The magnitude of the storm's destructive power was felt in equal measure along the shoreline of neighboring Mississippi, where glitzy casinos, plush homes and shrimp fishing businesses lay in ruins, after a storm surge up to 30 feet (10 meters) high crashed ashore Monday.

"This is our tsunami," said AJ Holloway, mayor of the devastated resort city of Biloxi, where a tidal surge swept away bridges, sent boats crashing into buildings and flooded entire neighborhoods.

"You're going to be looking at hundreds dead along the coast of Mississippi," Biloxi spokesman Vincent Creel said.

Authorities said at least 50 people were known to have been killed in Biloxi alone, around 30 of them in a single apartment complex demolished by the storm.

A million people were without power across Mississippi, Louisiana and Alabama, water supplies were compromised and collapsed communications left large areas cut off from the outside world.

Damage estimates soared into the billions of dollars and oil prices raced to the historic level of 70.85 dollars per barrel on anxiety over damage to US facilities, many of which are on the Gulf Coast.

Governor Blanco told CNN that the US Army Corps of Engineers was working on trying to repair the levees in New Orleans.

Officials warned of large numbers of gas leaks. Fires could be seen burning out of control in several areas.

About 3,500 Army National Guardsmen in Louisiana will help with security, shelter, removing debris and distributing water and food, said spokesman Jack Harrison. More than 850 National Guardsmen in Mississippi have been activated, he said.

PHOTO CAPTION

A lumber and paper building is destroyed and scattered in Pascagoula, Mississippi, August 30, 2005 after Hurricane Katrina hit. (REUTERS)