At least seven people were killed after part of a boat dock collapsed, sending at least 20 into the Atlantic waters off the coast of the US state of Georgia.
US Coast Guard ships were searching on Saturday night for missing people.
The accident, which also caused multiple injuries, happened during a celebration of Sapelo Island's tiny Gullah-Geechee community of black slave descendants, authorities said.
A gangway crowded with people waiting for a ferryboat collapsed late on Saturday afternoon on the Georgia barrier island about 100 km south of Savannah, said Tyler Jones, a spokesperson for the Georgia Department of Natural Resources, which runs the ferry.
"We and multiple agencies are searching for survivors," Jones said.
Vice President Kamala Harris, in the state capital Atlanta for campaign events, issued a statement late on Saturday, saying the Biden administration was in close touch with state and local officials and had offered any federal support needed.
"Tonight, Doug and I are praying for all those who were killed or injured in the collapse of the ferry dock walkway on Georgia’s Sapelo Island, as well as their family members and loved ones," Harris said, referring to her husband, Doug Emhoff.
"Even in the face of this heartbreak, we will continue to celebrate and honour the history, culture, and resilience of the Gullah-Geechee community," she added.
Coast Guard helicopters and boats equipped with sonar immediately began search-and-rescue operations, officials said. The cause of the accident was not immediately clear.
Sapelo Island is only reachable by boat, and the state-run ferry takes about 20 minutes to reach its shores.
People were marking Cultural Day, an annual festival celebrating the island's historic Black community, one of several surviving island communities from Georgia to North Carolina.
The people known as Gullah, or Geechee in Georgia, are believed to have retained much of their African heritage because of their isolation.
"Our thoughts and prayers go out to all involved, including the entire Sapelo Island Community," the Georgia Department of Natural Resources said in a statement.
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