Authorities are working to identify 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.

There were life jackets bobbing in the water, people forming a human chain to pass survivors to safety and bodies being carried ashore in blankets.

The aluminum gangway suffered structural failure as historic Sapelo Island hosted an event celebrating its Gullah Geechee history and culture.