Two people were unaccounted for after a Ride the Ducks tour boat capsized and sunk after colliding with a 250-foot barge in the Delaware River Wednesday.

The accident, in which 35 passengers and two crewmembers were tossed into in the 82-degree water, happened off Penn's Landing in Old City near the Independence Seaport Museum between Walnut and Chestnut Streets on the river at about 2:39 p.m., officials said.

The Ride the Ducks amphibious landing craft stalled in the water after a fire began in the boat's engine, said Philadelphia Police Lt. Frank Vanore. The boat drifted in the river for about 20 minutes when it collided with the barge, split into two and sunk. Sources on board said the boat flipped after a "huge metal object" hit the vessel.

Rescue crews, including the U.S. Coast Guard, Philly Police and city firefighters, were pulling passengers of the popular tour ride out of the river around 3 p.m. Passengers visible to Chopper 10 had life jackets on but sources told NBC Philadelphia that not everyone had on a life vest when the boat capsized.

Several visiting Navy SEALs were credited with being the first to jump into action. The SEALs were on their way to an event promoting a new program called Navy Seal Grove when they heard about the accident and rushed to the scene, Navy officials told NBC News.

The special forces officers used small ZODIAK boats to zip through the area and pluck people from the water.

Thirty-five of those onboard were rescued, but two young people remained missing hours after the accident.

A 16-year-old girl and 20-year-old man who were part of a large group of Hungarian tourists were said to be those missing, sources told NBC Philadelphia.

The Hungarians were visiting the area as part of a missionary exchange program operating out of the Marshallton United Methodist Church in West Chester, Pa.

Church Pastor Scott Widmer said the group arrived in the area last Thursday and were staying with families of the church's youth ministry.

A triage station was set up at the Independence Seaport Museum following the accident. At least nine passengers were brought to local hospitals with minor injuries, officials said.

Hahnemann University Hospital officials confirmed that eight people including two adults, three teens and three children were evaluated. A family was seen entering Hahnemann with duck whistles around their necks. At least one other passenger was taken to Jefferson University Hospital.

All those transported to both hospitals were released by late Wednesday evening, officials said.

The location of the sunken vessel was initially unknown to rescuers. It was later discovered by the Coast Guard around 6:30 p.m. in about 40-foot-deep water. Officials say they used sonar to find it in the murky waters of the river.

Divers made their way down to the boat, but were unable to explore the wreckage in detail because it was too unstable. The Coast Guard says they will not attempt to raise the vessel, but that Ride the Ducks can do so as part of a private recovery mission.

Here is a map of the area where the accident took place:

[googlemaps https://maps.google.com/maps/ms?ie=UTF8&hl=en&t=h&msa=0&msid=104224171039350228409.00048ad116582515418a8&ll=39.949622,-75.137686&spn=0.005757,0.00912&z=16&output=embed&w=425&h=350]



View Ride The Ducks Accident in a larger map

The icon at the top of the map shows where the Duck vessels enter and exit the river at Race Street. The red area highlights the accident zone and the icon at the bottom of the map shows the location of the triage center.

Authorities shut down the river to all recreational traffic as they searched the waters for the two missing people. As of late Wednesday, neither had been recovered.

The Ride the Ducks tour boat is an amphibious vehicle that can drive on city streets and then float in the river. It's well known by locals for the quacking devices tourists are given to blow on while they ride around town on 70-minute tours of the city's historic district.

The 18-foot-vehicles are remakes of GM's original 6-wheeled DUKWs built for the U.S. Army during World War II.

Just last week NBC Philadelphia's own Lu Ann Cahn rode the Ducks as part of her One Year of Firsts campaign. See her story here to get a feel for what it is like.

The tour company issued a short statement following the accident saying they've suspended operation for the time being.

Our thoughts and prayers are with our Philadelphia tour guests, crew members and their families. We are attending to their needs first. In the interim, we have suspended our operation in Philadelphia.

According to the Ride the Ducks website, the vehicle is equipped with life jackets for adults and children passengers.

"By the way, we have never had to use any of them, but you can never be too prepared," the site states.

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