The Association of American Museums' (AAM) website reported museums and historical houses that had been flooded, gutted and, in some cases, even raised to the ground.

Edward Able, the president of the AAM, said: 'I don't think we've ever in our history had an actual threat to our cultural patrimony of this scope.'

The Mississippi Heritage Trust provided disturbing photos documenting the extent of the damage to historic houses and sites in the region on its website.

At Beauvoir - the home of the only president of the Confederate States of America, Jefferson Davis - the first floor of the presidential library was destroyed. Patrick Hotard, the director, said artefacts were removed before the storm and although the main structure still stands, there was substantial damage to the site.

Dantzler House in Biloxi, which had recently been refurbished and was about to open as a Mardi Gras Museum, was obliterated.

Also in Biloxi, a casino barge crushed part of the Ohr-O'Keefe Museum of Art, which was under construction. The $30m (£17m) project was designed by Frank Gehry and was due to open next year.

Although many museums and galleries escaped the storm with only minor damage, the heat and humidity is now threatening objects. Power supplies have not returned to normal and the fear is that lack of power and staff will hamper the salvage operation.

'The problem is these institutions made it through the storm, but the worst may be yet to come,' said Able.

AAM said the response from museum professionals across the US had been 'warm and helpful' and offers of help ranged from storage space to conservation assistance.

John Zvereff, the secretary general of the International Council of Museums (ICOM), said that ICOM would coordinate offers of assistance from around the world.

He told Museums Journal that his organisation had not yet received any calls for assistance, but that the Disaster Relief Fund, which was set up to help museums following the Tsunami at the end of last year, was not just for museums in the developing world.

'What happened in Louisiana shows countries that have previously set the tone in museum development are not exempt from disaster.'

For up-to-date news about museums and galleries affected by Hurricane Katrina, visit: www.aam-us.org/aamlatest/news/HurricaneFirstReports.cfm; www.mississippiheritage.com/HurricaneKatrina.html; or www.icom.museum/disaster_relief/

Sharon Heal