A security guard patrolling the waterfront said he saw the accident while making his rounds, spinning around after he heard the screams of other bystanders who saw it first.
"I whirled around as the barge began to run over the duck boat," said Larry Waxmunski, a guard for the Delaware River Waterfront Corp. "After the barge hit it -- it almost looked like slow motion -- the duck boat began to turn over."
"Fortunately, you began to see the life vests popping up almost immediately," Waxmunski said. He then saw police boats beginning to pluck the tourists out of the water.
Television footage showed at least five people being pulled from the water wearing life vests in an area of the river near the Old City neighborhood, popular with tourists. Helicopter footage showed people in life vests being helped from boats on to a dock and at least one person on a gurney.
Terri Ronna, 45, of Oakland, N.J., said she was on a ferry going from Camden, N.J., across the river to Philadelphia when the captain announced that there was someone overboard from another ship and that they were going to rescue him.
"We were not even halfway over when they said there was somebody overboard and we were going to get them," Ronna said. "There were people all over; we could see all these orange life vests."