While army engineers fought to fill huge breaches in levees designed to waters out of New Orleans, looting broke out and gas leaks caused many fires. The city's mayor warned it could be up to four months before evacuated residents could return.

The US government said, meanwhile, it would release oil from an emergency reserve in a bid to ease international worries of shortages caused by the devastating storm.

Fears of a major death toll grew as the scope of the devastation became more apparent.

Vincent Creel, a city spokesman at Biloxi, Mississippi, estimated that hundreds of people may have been killed along the Mississippi coastline from Pascagoula to Gulfport, including Biloxi.

An emergency management director told the Clarion Ledger newspaper there were 100 confirmed deaths in Harrison County, Mississippi alone.

Authorities told rescuers to leave bodies to one side and concentrate on finding survivors trapped on roofs and in the attics of homes where many people took shelter when 200 kilometer (125 mile) an hour winds crashed into the coast on Monday.

Mississippi Governor Haley Barbour said that 90 percent of buildings in the worst-hit area of the Gulf Coast in his state are "totally just gone".