SEVERAL construction workers were trapped underground after a tunnel collapsed in Los Angeles.

The 31 men were caught inside the structure nearly 450 feet below ground on Wednesday night, launching a full-scale rescue by firefighters.

The incident occurred shortly before 8pm at the location of the Los Angeles Effluent Outfall Tunnel, valued at $630.5 million and part of the LA County Sanitation District’s Clearwater Project.

Crews were working more than six miles from the tunnel’s only access point when disaster hit.

The Los Angeles Fire Department reported that the trapped workers were able to climb over a 12 to 15-foot mound of loose soil to reach their coworkers on the opposite side of the debris.

They then accessed a tunnel vehicle, which transported them five miles to the tunnel’s only vertical shaft, offering the sole exit from the enormous structure.

The workers were then lifted to safety in groups of eight using a crane-mounted elevator known as a “bird cage”.

The LAFD said in a statement: “Preliminary reports are that the trapped workers were able to scramble with some effort over a 12-15’ tall (undetermined length) pile of loose soil, to meet several coworkers on the other side of the collapse, and be shuttled several at a time by tunnel vehicle to the entry/access point more than five miles distant.”

By 9.20pm local time, all 31 were safely above ground, with many hugging each other in relief, KTLA reported.

No injuries were reported, but 27 were evaluated by paramedics on site.

More than 100 LAFD responders, including specialised Urban Search and Rescue teams, were dispatched in what officials feared could have turned into a multi-day operation.

LA Mayor Karen Bass said in a post on X: “I just spoke with many of the workers who were trapped.

“Thank you to all of our brave first responders who acted immediately. You are L.A.’s true heroes.”

The tunnel, 18 feet in diameter and set to stretch seven miles, is being constructed to replace ageing wastewater infrastructure dating back to 1937.

Work began in 2021, and prior to the collapse, tunnelling was expected to finish by the end of this year, with the full project complete by 2027.

The cause of the collapse remains under investigation.

Wednesday’s near-tragedy marks the first major incident since construction began.

Officials say the response — and the workers’ own quick thinking — helped avert what could have been a deadly disaster.