LOS ANGELES – 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.

None of those rescued had major injuries, authorities said.

Arally Orozco said she was at church when her phone started buzzing with calls and then her son texted her the news of the tunnel where her three brothers worked.

“It was sad and scary,” she said in Spanish. “We feared the worst.”

After an hour, she managed to get through to one brother who told her they had to squeeze through a tight space to get out.

“My brother was crying,” she said. “He told me he thought he was going to die underground.”

LA City Councilmember Tim McOsker praised the workers for keeping cool heads.

“This is a highly technical, difficult project. And they knew exactly what to do. They knew how to secure themselves,” he said. “Thank goodness for the good people that were down in the tunnel.”

Mayor Karen Bass said at a news conference that she met with some of the workers.

“I know when we raced down here I was so concerned that we were going to find tragedy. Instead, what we found was victory,” Bass said. “All of the men that were in that tunnel, rescued, up, safe.”

The tunnel is being constructed almost entirely underneath public right-of-way. The structure is 18 feet (5.5 meters) wide and will be 7 miles (11.3 kilometers) long to carry treated wastewater from across Los Angeles County to the Pacific Ocean.

Work will not resume until the project contractor assesses what happened and deems the site safe, authorities said.