PORT-AU-PRINCE, Aug 17 (Reuters) - Around 50 people died in Haiti on Sunday when a bus tried to cross a river swollen with rain from Tropical Storm Fay and was swept away, witnesses said.

Two dozen survivors were pulled alive out of the raging waters of the Riviere Glace in the southwestern province of Grand-Anse, said mayor Oreste Andre of the town of Bomont, where the accident occurred.

"The river swept them away as if they were driftwood," Andre said by telephone. He said the people who were rescued survived by climbing onto the roof of the sunken bus. The dead were trapped inside.

Thema Laurent, an eye witness who had been waiting on the banks along with other drivers for the river to calm down, said a child was among the survivors but a dozen children on board failed to make it out.

There were 80 or more people crowded on the bus headed to Jeremie, the largest city in Grand-Anse, Laurent and Andre said.

Four people were killed in Haiti on Saturday by the tropical storm as it passed over on its way to Cuba and Florida, possibly as a hurricane. One person was killed in the neighboring Dominican Republic and two were missing. (Reporting by Joseph Guyler Delva, editing by Michael Christie and Jackie Frank)

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