Police agencies to the south of New Orleans were so fearful of the crowds trying to leave the city after Hurricane Katrina that they sealed a crucial bridge over the Mississippi River and turned back hundreds of desperate evacuees, two paramedics who were in the crowd said.

The paramedics and two other witnesses said officers sometimes shot guns over the heads of fleeing people, who, instead of complying immediately with orders to leave the bridge, pleaded to be let through, the paramedics and two other witnesses said. The witnesses said they had been told by the New Orleans police to cross that same bridge because buses were waiting for them there.

Instead, a suburban police officer angrily ordered about 200 people to abandon an encampment between the highways near the bridge. The officer then confiscated their food and water, the four witnesses said. The incidents took place in the first days after the storm last week, they said.

"The police kept saying, 'We don't want another Superdome,' and 'This isn't New Orleans,"' said Larry Bradshaw, a San Francisco paramedic who was among those fleeing.