The deployment of 300 members of the Arkansas National Guard came ahead of a tour of the affected region by President George W. Bush, who vowed "zero tolerance" for the armed gangs terrorising the flooded city.

Louisiana Governor Kathleen Blanco said the guardsmen had been authorized to open fire on "hoodlums" profiteering from the destruction wrought by Hurricane Katrina, which is believed to have left thousands dead.

"These troops are fresh back from Iraq, well trained, experienced, battle tested and under my orders to restore order in the streets," Blanco said.

"They have M-16s and they are locked and loaded.

"These troops know how to shoot and kill and they are more than willing to do so if necessary and I expect they will," she said.

Four days after the killer storm slammed into the US Gulf Coast, New Orleans was still plagued by gunbattles and rapes, with gangs of looters and carjackers roving the streets and bodies just left lying by the roadside.

Residents reported survivors dropping dead in shelters or gunned down outside the New Orleans convention center. Hospitals were evacuated after power ran out and helicopters ferrying patients and babies drew gunfire.

"This is a war zone," said Melissa Murray, 32, a Louisiana state corrections officer helping in the relief effort.

Around 200 frightened Japanese, European and American tourists, who had been thrown out of their hotel on Thursday morning, told how police fired over their heads as they attempted to get to buses to take them to safety.

New Orleans Mayor Ray Nagin issued an urgent plea for help for up to 20,000 refugees stuck in the convention center which he said was "unsanitary and unsafe" and running out of supplies.

"This is a desperate SOS," Nagin said in a statement released through CNN television.

Blanco said up to 300,000 survivors may still be stuck in disaster areas in the state and at least 40,000 uniformed troops were needed for New Orleans alone.

Although no precise death toll was available, Blanco and Louisiana Senator Mary Landrieu said several thousand people were now believed to have been killed by Katrina.

Outside the New Orleans Superdome, thousands who had taken shelter in the stadium before the hurricane hit, were still trapped, waiting to board buses shuttling them to a new refuge in Houston, Texas.

But in a sign of the relocation problems to come, their intended destination, the Houston Astrodome, was already filled to capacity by Thursday evening with local officials diverting evacuees to other cities.

A National Guardsman was shot outside the Superdome and a shot was also fired at a Chinook helicopter taking part in the operation to move refugees out, officials said.

Amid reports that two children had been raped at the stadium, many people were outraged after spending four days without proper food, water and sanitation and enduring nights of lawless blackout.

"The last few days were utter hell. We were treated like animals," said Baron Duncan, 42.

The lawlessness distracted from frantic efforts to evacuate the city, where Nagin took hundreds of exhausted police off search and rescue duties to fight the looting gangs.

The US Senate, meeting in an extraordinary late night session Thursday, voted unanimously to authorize 10.5 billion dollars in special funding for hurricane victims, and the House of Representatives was expected to approve the measure on Friday.

But anger over the government response to the catastrophe remained vocal and widespread.

"This is a national disgrace," said Terry Ebbert, head of New Orleans' emergency operations.

Ebert said the Federal Emergency Management Agency had been in the city for 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 the city of New Orleans."

Thomas Jessie, a 31-year-old roofer, vented his fear and anger after spending a night in the squalor of the convention center with no National Guard or Red Cross workers in sight.

"We got dead bodies sitting next to us for days. I feel like I am going to die. People are going to kill you for water," Jessie told AFP.

Bush, who was scheduled to tour Louisiana, Misissippi and Alabama on Friday, called for public forbearance as relief efforts gathered pace.

"We all know this is an agonizing time for the people of the Gulf Coast. I ask their continued patience as recovery operations unfold," the president said. "This recovery is going to be a long process."

Bush also appealed for Americans to conserve car fuel for the next few weeks. But US petrol stations saw panic buying and lengthening queues Thursday as a summer of pain for drivers battling sky-high oil prices intensified.

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