Armed gangs broke into hospitals, offices, homes and shops, some in search of food, others looking for valuables to steal.

There were reports of carjackings, widespread looting and fights breaking out among the desperate and hungry.

Corpses were left lying in the streets and rescue helicopters trying to help the sick and injured were shot at.

Anger has been mounting since the hurricane struck on Sunday, killing thousands and leaving swathes of the city under water. Up to 5million people are still without power, while drinking water and food are running out.

George W Bush acknowledged that the damage to the city was worse than that suffered by New York in 9/11.

But he called for a zero tolerance approach towards law-breakers.

Earlier, 1,400 of the city's police officers were ordered to abandon search and rescue efforts to try to restore order.

'The looting started with people running out of food and you can't really argue with that too much,' said mayor Ray Nagin said.

'Then it escalated to this kind of mass chaos.' At one point, police stranded on the roof of a hotel were fired at from the street.

Thousands of extra National Guard troops were also being drafted in.

Inside the now stinking Superdome, initially a safe haven for the homeless, fights and fires broke out and shots were fired at a military helicopter.

Mississippi Governor Haley Barbour said: 'The truth is, a terrible tragedy like this brings out the best in most people, brings out the worst in some people.'

But outside a convention centre, where 20,000 people waited for buses to take them out of the city, the Rev Issac Clark, 68, said 'We are out here like pure animals. We don't have any help.'