The evacuation of the Superdome in New Orleans was suspended on Thursday after shots were reported fired at a military helicopter and arson fires broke out outside the arena.
No immediate injuries were reported.
Thousands are holed up at the Superdome after Hurricane Katrina wrecked havoc.
The scene at the Superdome became increasingly chaotic, with thousands of people rushing from nearby hotels and other buildings, hoping to climb onto the buses taking evacuees from the arena, officials said.
The sight of people with guns increasingly alarmed paramedics.
Richard Zeuschlag, chief of the ambulance service that was handling the evacuation of sick and injured people from the Superdome, said it was suspending operations "until they gain control of the Superdome."
He said shots were fired at a military helicopter over the Superdome before daybreak.
He said the National Guard told him that it was sending 100 military police officers to restore order.
"That's not enough," Zeuschlag said. "We need a thousand."
Lt. Col. Pete Schneider of the Louisiana National Guard said the military-- which was handling the evacuation of the able-bodied from the Superdome-- had suspended operations, too, because fires set outside the arena were preventing buses from getting close enough to pick up people.
He said tens thousands of people started rushing out of other buildings when they saw buses pulling up and hoped to get on. But the immediate focus was on evacuating people from the Superdome, and the other refugees were left to mill around.
Zeuschlag said paramedics were calling him and crying for help because they were so scared of people with guns at the Superdome.
He 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 100 people were on the landing pad, some with guns.
"He was frightened and would not land," Zeuschlag.
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