Armored military vehicles and National Guard troops started moving into New Orleans Thursday amid continuing reports of violence and chaos, including shots fired at the Superdome that interfered with an evacuation there after only a few hundred people had been moved out to Houston and other reports of gunfire aimed at rescuers.

Tempers appeared to be growing short in a variety of areas where hurricane survivors were gathered. Televised images of the area around the city's convention center showed angry crowds, who cursed at local officials, and a number of corpses out in the open because people there said they had nowhere to send the bodies.

Thousands of refugees from locations other than the Superdome --including downtown New Orleans hotels -- tried Thursday to join the exodus from the city, significantly increasing the numbers who need to be transported. Some non-Superdome refugees turned up on their own at Houston's Astrodome but were initially turned away.

Terry Ebbert, head of New Orleans's emergency operations, bitterly complained about the situation, criticizing the response from the Federal Emergency Management Agency. "This is a national disgrace," he told the Associated Press. "FEMA has been here three days, yet there is not command and control. We can send massive amounts of aid to tsunami victims but we can't bail out the city of New Orleans."

Military helicopters were continuing an operation begun last night to fly the sick and wounded from New Orleans to hospitals across the region. All but a few of New Orleans' hospitals were rendered inoperative because of flooding, which took out back-up generators.

But some of the efforts were being hampered by gunfire, according to a variety of reports, few of which could be independently confirmed.

"Hospitals are trying to evacuate," Coast Guard Lt. Cmdr. Cheri Ben-Iesan, told the AP. "At every one of them, there are reports that as the helicopters come in people are shooting at them. There are people just taking potshots at police and helicopters, telling them, 'You better come get my family.' "

Dr. Francesco Simeone, of Charity Hospital, said in a telephone interview on CNN that he had been told National Guard troops were ferried into that neighborhood after shots were fired today, but he said he had no direct knowledge of the shooting or if it was aimed at rescue operations. About 150 of the most critically ill patients have been removed from his hospital, but 350 patients and 600 staff members and their families remain in the facility, which he said is surrounded by waist-deep water. The evacuation has been halted, however.

At the Superdome, long lines of people waited for evacuation buses as helicopters buzzed through the sky, and thousands more people gathered at the convention center and lined highways hoping for a ride out of the city -- or even some information about what to do.

Some frustrated residents complained that no one seemed to be in charge.

"We've been trying to get out," said Cornelius Washington as he walked along a highway overpass near the Superdome. "No one is giving the who, what, where, why and when. When they give us information, it's about what they're not going to do."

Washington said he had some money but could not find anyone he could pay to take him to Baton Rouge or anywhere else. He was trying to make his way to the Superdome, where buses were arriving in waves to take people to Houston. But authorities at the overwhelmed stadium were accepting no new evacuees other than the 23,000 who had gathered there before the evacuation started Wednesday night.

The mounting frustration was illustrated by an incident at the Superdome around 3:30 a.m. Thursday when three out-of-town buses pulled up. Anxious refugees trying to board the buses began banging on them, and the drivers grew frightened and pulled away empty, one witness said.

At the convention center about a mile from the Superdome, thousands of people gathered after being told Wednesday to go there for relief, only to find no one in authority to hand out water, food or information.

As stranded residents made their way on foot to highways to wait for someone to pick them up, National Guard trucks began rescuing some people and taking them out of the city.

Amid signs of growing lawlessness, with looters roaming the city with impunity, heavily armed state and local police made a show of force in some places. Police in body armor and carrying shotguns and assault rifles were posted in the French Quarter and other parts of downtown to try to keep order.

In a briefing for Pentagon reporters in Washington, Army Lt. Gen. Russel L. Honore, the commander of a hastily-formed military unit called Task Force Katrina, said National Guard forces -- now numbering 4,700 in Louisiana and 2,700 in Mississippi -- will be strengthened to a combined 24,000 over the next three days.

"That capability is on the road as we speak, flowing to Mississippi and Louisiana," said Honore, who commands the First U.S. Army in Fort Gillem, Ga.

Honore said two battalions of troops from Fort Hood, Tex., have also been deployed to help support operations in Louisiana.

He said the majority of National Guard forces going to Louisiana "are security-type forces."

Honore said that roughly 60,000 inhabitants remained in New Orleans. "A large number of them are at the Superdome, but people are still scattered in their communities in isolated areas," he said.

Most of the city's 485,000 residents heeded a mandatory evacuation order issued Sunday as Hurricane Katrina bore down on the Gulf Coast.

One of those who made it to Houston was Rhonda Calderon, who arrived crammed in a Nissan Maxima with seven other people after a 14-hour drive.

"We have nowhere to go, nowhere to sleep," she told the Houston Chronicle. "We came to Houston seeking shelter. Our kids are hungry. We have no gas. What do we do?"

While there were mounting reports in local papers of people discovering floating bodies, there was still no officially confirmed death toll in any state.

"We understand there are thousands of dead people," Sen. Mary Landrieu (D-La.) said at a news conference in Baton Rouge.

Tommy Longo, the mayor of Bay St. Louis, Miss., estimated that at least 50 residents died, according to the Jackson Clarion-Ledger.

"Between the coast and the railroad, for an area of about 50 miles, there's nothing standing" in coastal Mississippi, said the state's governor, Haley Barbour (R). "We've rescued a lot of people but underneath that debris, it's realistic to believe there are going to be more people."

Rep. Richard Baker (R-La.), who represents the Baton Rouge area and was visiting a shelter there hold 5,000 evacuees, said he has appealed to the federal government to send in mobile military barracks to help shelter refugees who have come to the state capital from New Orleans.

"This is twice the scope of 9/11," he said, referring to the terrorist attacks on New York and the Pentagon. "The people of America don't understand that we need help. We need money."

Meanwhile, elected leaders from the president on down faced aggressive questioning on morning TV shows about the pace of rescue and relief operations.

President Bush, in a rare appearance on morning television, said he understood the "frustration" of people at the pace of relief in the area affected but said "this is a natural disaster the likes of which our country has never seen before. . . . New Orleans is more devastated than New York was" after the terrorist attacks of Sept. 11, 2001. "So we've got a lot of work," he said on ABC's "Good Morning America."

"But given the fact that everyone anticipated a possible [Category 5 hurricane] hitting shore," Diane Sawyer asked him, "are you satisfied with the pace at which this is arriving and which it was planned to arrive?"

"Well, I fully understand people wanting things to have happened yesterday. . . . I mean, I understand the anxiety of people on the ground. . . . I don't think anybody anticipated the breech of the levees," Bush said. "They did anticipate a serious storm. But these levees got breached and, as a result, much of New Orleans is flooded and now we're having to deal with it and will."

Bush will travel Friday to the region devastated by Hurricane Katrina, the White House said Thursday.

Buses from the Superdome began arriving at Houston's Astrodome early Thursday morning. News reports from Houston said the travelers looked exhausted and dazed. Some have been in the Superdome for as long as five days, most of the time without air conditioning or working toilets.

There were conflicting reports about whether the evacuation had been suspended, but Louisiana National Guard Lt. Col. Pete Schneider, speaking on CNN, said it was suspended briefly early Thursday morning after shots were fired at helicopters in the vicinity. He also said a guardsman was shot Wednesday night inside the Superdome. But officials said later in the day that rescue and relief operations were continuing.

Tens of thousands of hot, weary and hungry evacuees have been holed up in the Superdome for days. Thousands more have sought refuge in nearby hotels, even though they lacked power and water.

Schneider said hotel-bound refugees converged en masse on the Superdome Thursday morning hoping to get on buses headed for Houston, raising the total needing transportation from about 25,000 to as many as 40,000.

Richard Zuschlag, head of Acadian Ambulance, which was handling the evacuation of sick and injured people from the Superdome, told the Associated Press that shots were fired at a military helicopter over the Superdome before daybreak.

Zuschlag also said that during the night, when a medical evacuation helicopter tried to land at a hospital in the outlying town of Kenner, the pilot reported that 100 people were on the landing pad, and some of them had guns. "He was frightened and would not land," Zuschlag said.

He added that medics were calling him and crying for help because they were scared of people with guns at the Superdome.

People were also setting small trash fires around the Superdome, where tens of thousands of people milled about restlessly.

Across the region, officials said they were desperately worried about what they would find once they are able dig beneath the wreckage left of thousands of homes and buildings from Louisiana to Alabama.

There remained massive shortages of food, water and fuel across the region. Even officials at the New Orleans Airport, a staging area for military and civilian rescue operations, lacked resources.

"We need diesel fuel. Gasoline. We need generators," said Charles Cazayoux, the airport manager. "We need manpower, from laborers to folks who can give us relief for our staff."

Staff writer Jaqueline L. Salmon contributed to this story from Baton Rouge. Barbash and Branigin reported from Washington.