At least seven people were killed after part of a ferry dock collapsed on Georgia’s Sapelo Island, authorities said.

Multiple people were taken to hospitals, and crews from the US coast guard, the McIntosh County Fire Department, the Georgia Department of Natural Resources and others were searching the water, according to spokesperson Tyler Jones of the Georgia Department of Natural Resources, which operates the dock.

Jones said a gangway at the dock collapsed and sent people plunging into the water. It happened as crowds gathered on the island for a celebration of its tiny Gullah-Geechee community of Black slave descendants.

“There have been seven fatalities confirmed,” Jones said. “There have been multiple people transported to area hospitals, and we are continuing to search the water for individuals.”

Jones said he did not know what caused the gangway to collapse, but officials believe there were at least 20 people on it at the time. The gangway connected an outer dock where people board the ferry to another dock onshore.

Among the dead was a chaplain for the Georgia Department of Natural Resources, Jones said.

Sapelo Island is about 60 miles (97km) south of Savannah and is reachable from the mainland by boat.

Cultural Day is an annual fall event spotlighting the island’s tiny community of Hogg Hummock, which is home to a few dozen Black residents. The community of dirt roads and modest homes was founded by former enslaved people from the cotton plantation of Thomas Spalding.

Small communities descended from enslaved island populations in the South – known as Gullah, or Geechee in Georgia – are scattered along the coast from North Carolina to Florida. Scholars say their separation from the mainland caused residents to retain much of their African heritage, from their unique dialect to skills and crafts such as cast-net fishing and weaving baskets.