Sporadic violence erupted in the hurricane ravaged New Orleans city forcing authorities to suspend evacuation as President George W Bush [Images] urged for "zero tolerance" for lawlessness and said the city suffered more damage than New York in the September 11 attacks.

• Thousands feared dead in New Orleans

A National Guardsman was reported shot and wounded outside the city's Superdome Stadium that housed upto 20,000 survivors.

Shots were also fired at a Chinook helicopter taking part in an operation to move refugees affected by Hurricane Katrina out of the stadium to other cities.

• NRI body to raise funds for Katrina victims

About 4,000 National Guard troops were being sent to the city to deal with the situation and more were being deployed to other towns on the Gulf coast, which has also seen widespread pillaging.

President George W Bush, who will tour the hurricane-devasted Gulf Coast on Friday, has asked his father, the former president George H W Bush and president Bill Clinton [Images] to lead a private fund-raising campaign for victims.

• Katrina Images

Bush said that while the September 11 terrorist strikes were a man-made disaster, its aftermath and that of Hurricane Katrina were "just as serious in both cases".

Bush spoke as thousands were evacuated on buses from a stadium in New Orleans to Houston. He expressed sympathy for those stranded. "Thousands have been rescued, there are thousands more to be rescued." He urged for a crackdown on looting and crime and said, "I think there ought to be zero tolerance of people breaking the law during an emergency such as this..."

• Evacuation halted amid gunfire

"New Orleans is more devastated than New York was," Bush told ABC Television adding, "just physically devastated as is the coast of Mississippi. So we've got a lot of work to do".

He said viewing entire neighbourhoods under water, as he did from the Air Force One on his way back to Washington on Thursday, was "very emotional... it is so devastating it is hard to describe it."

Bush said his emotions were somewhat different from September 11 because then he realised there were some killers who had killed Americans as opposed to the storm.

Though the exact number of the dead was not available, New Orleans Mayor Ray Nagin said thousands have perished in the disaster.

"We know there is a significant number of dead bodies in the water," as well as other people dead in attics." Asked how many dead, he said "minimum, hundreds. Most likely, thousands."

Nagin has ordered all residents to abandon the city and warned it will be months before people are able to return to their homes. The government has declared a public health emergency along the Gulf Coast and in Mississippi 110 people were confirmed dead, but officials warned the toll is expected to rise.

Earlier, looters went on a rampage in the ghost-city, forcing authorities to pull 1,500 policemen out of rescue and rescue operations to maintain law and order.

Residents reported hundreds of looters on the streets, armed robberies and car jackings. Several shots were also fired across the city, they said.