The gangway collapsed Saturday as festival goes prepared to board a ferry amid Sapelo Island's annual Cultural Day, officials say.

At least seven people are dead after a portion of a ferry dock collapsed at about 3:50 p.m. Saturday on Sapelo Island, authorities say. Twenty people fell into the water when a gangway to the dock collapsed, said Tyler Jones, a spokesman for the Georgia Department of Natural Resources, which operates the dock.

Investigators, including a team of engineers and specialists, are now on the scene to determine what caused the sudden collapse.

Authorities are investigating the cause of a partial ferry dock collapse on Georgia’s Sapelo Island that turned a day of celebration into tragedy, leaving at least seven dead and six critically injured as crowds gathered for a cultural festival.