At least seven people died and several others were hospitalized when a ferry dock walkway buckled in the US state of Georgia on Saturday, local authorities have said.

Eight people were hospitalized, at least six of them with critical injuries, the Georgia Department of Natural Resources (DNR) said in a statement, as quoted by the Associated Press.

A gangway, linking an outer dock where people board the ferry with another dock onshore, collapsed, sending about 20 people plunging into the Atlantic waters, according to Tyler Jones, a spokesman for the Georgia Department of Natural Resources. The department operates the dock and ferries that carry passengers between the island and the mainland.

Jones said crews from the US Coast Guard, the McIntosh County Fire Department, and others were searching the water for survivors. He added that a group of engineers and other experts would arrive on Sunday to investigate the cause of the disaster.

“There was no collision” with a boat or anything else, the spokesman said, as cited by the agency. “The thing just collapsed. We don’t know why.”