A frantic seach was under way in the Delaware River in Philadelphia today after a barge plowed into a tourist boat carrying 37 people, overturning the boat, authorities said.
As darkness fell and the search was halted for the night, at least two passengers were still unaccounted for. Six people were taken to hospitals with minor injuries. Police described the missing as a 16-year-old female and a 20-year-old male.
Investigators from the National Transportation and Safety Board say they are starting an investigation.
There were 37 people on the so-called "duck boat," an amphibious vehicle, when it collided with the passing barge at about 2:30 p.m. near Penn's Landing, Coast Guard Officer Crystal Kneen said.
"We do not know why these two vehicles collided," Mayor Michael Nutter told reporters at the scene. The National Transportation Safety Board was investigating.
But Philadelphia Police Commissioner Charles Ramsey said the tour boat entered the water about 2:30 p.m. just south of Ben Franklin Bridge and experienced "mechanical difficulties." A fire started on board and its engine shut down.
"The boat was sitting on the water waiting for help" at the time of the collision, Ramsey said.
Witnesses told investigators that some passengers tried frantically to get the attention of the approaching barge but were forced to jump into the river as the barge hit the boat. The barge was roughly 250 feet long, according to the Coast Guard.
Witnesses told ABC News Philadelphia station WPVI-TV that the boat was not moving, and appeared to be stuck or disabled before the crash.
Two Coast Guard boats, with the assistance of local police and fire crews, plucked people from the water.
At least five people in life vests could be seen on TV news footage being pulled from the water. Other news video showed some passengers being helped from boats onto a dock. One person was on a gurney.
"We are still actively searching for two people," Kneen said.
A security guard patrolling the waterfront told The Associated Press that 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 plucking tourists from the water.
Terri Ronna, 45, of Oakland, N.J., told the AP that 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."
In 1999, a Duck Boat took on water and sank in Lake Hamilton in Hot Springs, Arkansas, killing 13 of the 20 people on board. No one on the boat was wearing life preservers at the time. The Arkansas boat was owned by White & Yellow Duck Sightseeing Tours.
Duck boats, made famous as landing craft in World War II, are used by many local tour providers in the U.S. They navigate city streets as well as local waterways.
Philadelphia Duck Tours is operated by Ride The Ducks, a company that operates similar tourist trips on the amphibious vehicles out of other locations around the country, including San Francisco; Newport, Kentucky; Seattle; and Stone Mountain Park, Georgia, according to the company's website.