Thirty-one people working in a massive underground tunnel in Los Angeles were rescued Wednesday night after a portion of the structure collapsed, officials said. Those rescued didn’t have any visible injuries,

Workers were 400 feet (121 meters) underground and as much as 6 miles (9.6 kilometers) inside from the only entrance when the cave-in Wednesday evening threatened to trap them on the far side of the tunnel’s boring machine,

The Los Angeles Fire Department rushed to Wilmington after a tunnel collapsed and trapped 31 people inside. The construction workers inside the underground tunnel were rescued roughly an hour after the collapse, according to L.A. County Supervisor Janice Hahn, who represents the area.