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.

Fire officials said the trapped workers managed to escape by scrambling over a roughly 12- to 15-foot mound of loose soil to reach four co-workers who had gone in to help.

None of the 31 construction workers rescued in the tunnel sustained visible injuries, according to LAFD. Firefighters said construction workers climbed over a roughly 12 to 15-foot pile of dirt to escape.