An air ambulance service official said that helicopter transfers of the sick and injured were suspended, but the National Guard said that able-bodied evacuees were still being moved by bus to Houston's Astrodome.
"We have suspended operations until they gain control of the Superdome, " said Richard Zeuschlag, head of Acadian Ambulance, which was handling the evacuation of sick and injured people from the Superdome.
He said that military would not fly out of the Superdome either because of the gunfire and that the National Guard told him that it was sending 100 military police officers to gain control.
"That's not enough," he said. "We need a thousand."
He said that shots were fired at a military helicopter over the Superdome before daybreak.
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 that 100 people were on the landing pad, and some of them had guns.
"He was frightened and would not land," he said.
He said medics were calling him and crying for help because they were so scared of people with guns at the Superdome.
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.
Lt Col Pete Schneider of the Louisiana National Guard said the military - which was handling the evacuation of the able-bodied from the Superdome - temporarily suspended operations, too, because fires set outside the arena were preventing buses from getting close enough to pick up people.
He said tens of 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.