LOS ANGELES (AP) — Thirty-one construction workers inside a huge industrial tunnel in Los Angeles made it to safety after a portion of it collapsed Wednesday evening, an outcome officials called a blessing after they initially feared much worse.

The cave-in appears to have occurred between the tunnel boring machine 5 miles (8 kilometers) in from the sole entrance and the construction workers who were working 6 miles (9.6 kilometers) in, said Michael Chee, spokesperson for the Los Angeles County Sanitation Districts, which is in charge of the nearly $700 million project.

The workers were about 400 feet (121 meters) underground.

Authorities were still investigating the cause, Chee said.

The workers scrambled over loose soil more than 12 feet (19.3 meters) high to reach the tunnel boring machine and then were transported back to the opening. Aerial footage showed workers being brought out of the tunnel in a yellow cage hoisted up by a crane.