The mayor of New Orleans issued "a desperate SOS" yesterday as the effort to evacuate thousands of people still trapped in the flooded city was hindered by mob violence and gunfire.
The appeal came as angry crowds clashed with police, and the city's police chief warned that storm victims were being raped and beaten on the streets.
National guardsmen were moving into New Orleans in armoured vehicles to re-establish order and help the evacuation. But reports from the city described desperate scenes in the Superdome stadium and the city convention centre, where tens of thousands were awaiting evacuation, with fights breaking out, rubbish catching fire and dead bodies left uncollected.
According to the police chief, Eddie Compass, an angry mob drove back 88 officers who were sent to restore order.
"We have individuals who are getting raped, we have individuals who are getting beaten," he said. "Tourists are walking in that direction and they are getting preyed upon."
Hurricane Katrina, which struck America's Gulf coast on Monday, and the subsequent flooding of New Orleans, is believed by officials to have taken thousands of lives. It was clear yesterday the crisis was still not under control.
Aid officials said helicopter missions to evacuate patients from New Orleans hospitals had been suspended because some helicopters had come under fire, possibly from armed civilians angry they were not being rescued. According to a New Orleans report, a police station had come under attack on Wednesday night, and some policemen were leaving their posts yesterday afternoon.
President George Bush called for "zero tolerance" towards criminals and promised the federal government was doing everything possible to speed the rescue. But his administration was criticised by officials in Louisiana for not responding fast enough.
Buses began ferrying stranded people from the New Orleans Superdome to another stadium on dry land, the Astrodome in Houston. But the city's mayor, Ray Nagin, predicted there would not be enough buses to rescue people in the convention centre
"This is a desperate SOS," Mr Nagin said on CNN TV. "Right now we are out of resources at the convention centre and don't anticipate enough buses. We need buses. Currently the convention centre is unsanitary and unsafe and we're running out of supplies."
Anger was also mounting at the Federal Emergency Management Agency (Fema), which coordinates the national response to natural disasters.
Terry Ebbert, head of New Orleans's emergency operations, complained that Fema was not offering enough help.
"This is a national emergency. This is a national disgrace," he said. "Fema has been here three days, yet there is no command and control. We can send massive amounts of aid to tsunami victims, but we can't bail out New Orleans."
Officials said that 50,000 part-time national guard troops and military personnel would be committed to the relief effort. But the Pentagon resisted any suggestion that national guard troops from Louisiana should be pulled out of Iraq ahead of schedule.
Much of the unrest appeared to be driven by desperation as trapped survivors searched for food and water. Mr Bush made no distinction between those looters and the criminals stealing electronic goods.
"I think there ought to be zero tolerance of people breaking the law during an emergency such as this, whether it be looting, or price-gouging at the gasoline pump or taking advantage of charitable giving,," Mr Bush told ABC television. "If people need water and food, we're going to do everything we can to get them water and food. But it's very important for the citizens to take personal responsibility and assume kind of a civic sense of responsibility."
Unrest broke out in the Superdome, where more than 20,000 people have been awaiting evacuation. Conditions have been deteriorating after part of the roof was blown off and the toilets blocked. Fights broke out and rubbish caught fire. In a scuffle, a police officer was shot in the leg.
Last night CNN reported that a New Orleans hospital had stopped evacuations after coming under sniper fire.
A spokesman for the homeland security department, Russ Knocke, said: "In areas where our employees have been determined to potentially be in danger, we have pulled back."
"Hospitals are trying to evacuate," coastguard lieutenant commander Cheri Ben-Iesan said. "At every one of them, there are reports that as the helicopters come in people are shooting at them."
The president is due to make a tour today of the devastation from Louisiana to Mississippi and Alabama.
Baton Rouge, the Louisiana state capital, doubled in population overnight from 250,000 to over 500,000 as refugees poured in, according to a local councillor, Mike Walker.
"It's a new Baton Rouge," he said. "The unemployment rate in Baton Rouge is not very high. Now thousands of unemployed people are coming here. They are just being dropped off where they get off. They have no job, no cash."
It was also reported last night that the musician and New Orleans resident Fats Domino, 77, was missing following the hurricane.