Two tourists were feared drowned after their amphibious sightseeing bus sank on a Philadelphia river.

Divers were today searching for the 20-year-old man and 16-year-old girl who were among 37 people on the six-wheeled duck boat which was hit by a barge after its engine failed.

The rest were pulled from the river by other vessels in a frantic rescue operation after the accident.

The duck boat, which can travel on land and water, had driven into the river yesterday but was hit by a mechanical problem and a small fire.

It was struck about 10 minutes later by a barge used to transport sludge and sank to the bottom of the river.

The missing pair were members of a Hungarian tour group.

"Hope is fading, but we're not giving up hope completely," Coast Guard Capt. Todd Gatlin said night.

Ten people were taken to a hospital; two declined treatment, and the other eight were treated and released.

The National Transportation Safety Board said it planned to try to obtain any radio recordings, any possible mayday calls, photographs from witnesses or people aboard and other evidence.

It said investigators want to know why the vessels collided and how visible the duck would have been to the tug pushing the 250ft barge.

Police Commissioner Charles Ramsey said divers found the duck boat in about 50ft of water.

Some duck boats are amphibious military personnel carriers dating back to the Second World War that have been restored and reconditioned. Known by their original military acronym as DUKWs, they were first introduced in the tourism market in 1946 in the Wisconsin Dells, where about 120 of the vessels now operate.

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