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.

In the midst of a celebration of the island’s small Gullah-Geechee community of Black slave descendants, a gangway collapsed on the visitor ferry dock shortly before 4 p.m. Saturday and plunged at least 20 people into the water, Georgia Department of Natural Resources Capt. Chris Hodge said at a Saturday night news conference.

It remains unclear why the Marsh Landing Dock collapsed. A team of engineers and construction specialists plan to be at the dock early Sunday to begin investigating why it failed, Natural Resources spokesperson Tyler Jones told the Associated Press.

“The gangway has been secured on Sapelo Island and the incident is currently under investigation,” the Georgia DNR, which manages the island and operates the ferry service, said in a news release Saturday night. Ferries typically depart from the Sapelo-side dock three times a day, taking visitors to the mainland dock in Meridian.

Among those who died was a chaplain for the DNR, Georgia DNR spokesperson Melissa Cummings confirmed to CNN. Details about other people who died have yet to be released. Two of those injured were flown by air ambulance to hospitals for treatment, Hodge said.

The state’s natural resources department said multiple other emergency agencies assisted them by deploying boats equipped with side-scan sonar and helicopters for search and rescue missions. A reunification point was set up at an area church where those searching for family members can gather, the McIntosh County Sheriff’s Office said.

CNN has reached out to the McIntosh County Sheriff’s Office, McIntosh County EMS and the US Coast Guard for more information.

The tragedy happened during Gullah-Geechee Cultural Heritage Awareness Month, which is celebrated in October in the states of North Carolina, South Carolina, Georgia and Florida. The Sapelo Island Cultural And Revitalization Society, which hosts the island’s annual Cultural Day Festival, said it was grateful for the support people have shown.

“Our thoughts and prayers are with the families and loved ones who lost their lives and who were injured,” the nonprofit organization whose mission is to preserve Gullah-Geechee culture, land and community on Sapelo Island said in a Facebook post. “The Sapelo Island community is grateful for the outpouring of love and support and we ask that you join us in praying for the families of those who were impacted by this tragedy.”

The nearby city of Darien in McIntosh County said “a day of celebration has turned to tragedy following an accident.”

Both President Joe Biden and Georgia Gov. Brian Kemp said they were “heartbroken” over the news of the collapse in separate statements on Saturday. The tragedy comes after the island suffered damage during Hurricane Helene, including a six-day power outage, according to the Southern Poverty Law Center.

“Jill and I mourn those who lost their lives, and we pray for the injured and anyone still missing. We are also grateful to the first responders at the scene,” Biden said.

He added the White House is in touch with state and local officials to provide any assistance that would be helpful to the community.

“As state and local first responders continue to work this active scene, we ask that all Georgians join us in praying for those lost, for those still in harm’s way, and for their families,” Kemp said in a post on X.

Georgia Sen. Raphael Warnock said he was “deeply saddened” by the news out of Sapelo Island, saying it was “a tragic end to a joyous celebration.”

“Praying for the loved ones of those we sadly lost and those still missing,” he said in a post on X Saturday night. “The heart of every Georgian is with the Gullah Geechee community & the people of Sapelo Island tonight.”

‘Everyone is family’ in one of Georgia’s last Gullah-Geechee communities

Sapelo Island – a barrier island off the coast of Georgia accessible only by boat or ferry – is home to the Hog Hammock community of a few dozen full-time residents, according to Explore Georgia. Many of them are known as Gullah-Geechee people, who descended from enslaved Africans who were brought to the island in 1802 and worked on coastal plantations.

Hogg Hammock’s Gullah-Geechee community members are extremely close, having been “bonded by family, bonded by history and bonded by struggle,” Roger Lotson of the McIntosh County Board of Commissioners told the AP. His district includes Sapelo Island.

“Everyone is family, and everyone knows each other,” Lotson said. “In any tragedy, especially like this, they are all one. They’re all united. They all feel the same pain and the same hurt.”

Historians believe Hogg Hammock, which was listed in the National Register of Historic Places in 1996, is one of the last surviving Gullah Geechee communities in the Georgia Sea Islands. The extremely tight-knit community has retained many of their West African cultural traditions and languages, passing them from one generation to the next. That includes practicing the ancient African art of basket making, keeping alive the ring shout music folk tradition, making a living by fishing shrimps and harvesting oysters, and speaking in an English-based creole vernacular known as Gullah.

On Saturday, island residents and visitors attended the six-hour-long Cultural Day that honored those Gullah-Geechee traditions with African dance performances, native food vendors and historic tours.

Jerald J. Thomas, a pastor at Elm Grove Church near the site of the collapse, told CNN affiliate WTOC that the community came together to help after the tragedy.

“They came together quickly, and they began to send the necessary things that was needed in order to make the people’s stay, while they were going through this tragic time, more bearable,” Thomas said.

A number of island residents are older and on fixed incomes, Sapelo Island descendant Josiah “Jazz” Watts, previously told CNN. Last year, a zoning change raising the maximum square footage of a heated-and-cooled house was met with concern by residents who said it would allow the wealthy to build properties in the community and lead to high property taxes.

Only 29 original descendants are left in the community, Maurice Bailey, a local historian and ninth generation Hogg Hammock resident, told CNN last year. He estimated that descendants own 63% of the properties and 75% of the acreage on Sapelo Island.