Initial tests suggest the putrid waters flooding New Orleans, which are still several feet deep, are awash with E coli and 10 times the safe level of other bacteria. Epidemics of cholera, typhoid, malaria and West Nile virus are anticipated.

Makeshift mortuaries have begun dealing with the bodies but many are so disfigured they will never be identified. Some 96 Britons are still missing, according to the Foreign Office.

People reluctant to leave the city are being warned of the grave health risks. Coastguard chief of staff Thad Allen said: "Today we will go block by block through the city, requesting people to leave. It is unsafe and we need everybody out so we can continue the work of restoring this city."

Stinging Criticism

Initial tests suggest the putrid waters, which are still several feet deep, are awash with E coli and 10 times the safe level of other bacteria. Epidemics of cholera, typhoid, malaria and West Nile virus are anticipated.

The dangers are not limited to the worst-hit areas. Viruses are easily transmitted and pose a greater risk to evacuees in densely packed shelters.

Houston Astrodome, where 16,000 sought refuge after the disaster, now houses fewer than 3,000 as people are leaving in an attempt to rebuild their lives. It is expected to be cleared by next Sunday. Those remaining will be given $2,000 (pounds 1,000) debit cards to buy essential items, such as toiletries and food. The Red Cross is also giving out its own debit cards.

The body bags were ordered by the Federal Emergency Management Agency (FEMA), which has come in for stinging criticism for its slow reaction to the disaster.

President George Bush is expected to ask Congress for $51.8 billion (pounds 28bn) for the next stage of recovery. It follows $10.5 billion (pounds 5.7bn) aid already approved. About 400,000 jobs could be lost this year because of the hurricane, according to a congressional report. Early estimates suggest it could cost the government at least $100 billion (pounds 55bn).

International Aid

The US yesterday asked NATO to take on a bigger role transporting European aid to areas hit by Hurricane Katrina. A special meeting of the allies immediately ordered military experts to draw up plans for an expanded role, including the possible use of ships from the elite NATO Response Force.

European nations have made substantial offers of food, medicine, bedding and other help. Some non-NATO nations, such as Russia and Switzerland, have also been co-ordinating their aid through the NATO center.

US principal deputy assistant Secretary of State for European and Eurasian Affairs Kurt Volker said: "We are extremely grateful for the generosity and the contributions being offered by countries in Europe and countries throughout the world."