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A construction worker was killed in a grim accident Wednesday in Hermosa Beach after he fell head first into an excavated hole that collapsed around him, police and fire officials said.

State investigators found that the contractor did not have a permit to excavate the site, located at Sixth and Cypress streets.

The worker, who has not been identified, was standing on a plywood platform placed on the fork of a Bobcat Caterpillar raised about 6 feet above the ground, and about 15 feet above the bottom of the hole, said Cal/OSHA spokeswoman Krisann Chasarik.

He was using a hand-held compactor that works like a jackhammer to push down a steel pile for a retaining wall, investigators said. The vibration from the tool caused him to fall head first into the narrow hole, Chasarik said.

A substantial amount of soil that had been piled above the open trench then collapsed on top of him, said Capt. Mike Garofano of the Hermosa Beach Fire Department. Only a portion of the man's leg and foot were exposed, said Hermosa Beach Police Detective Mick Gaglia.

It was not clear what caused the soil above to fall, but investigators noted that it was very unstable, Chasarik said.

Dozens of emergency workers were on the scene for most of the day Wednesday attempting to dig the victim out. The Los Angeles County Fire Department's specialized Urban Search and Rescue unit was called for assistance due to the danger of the unstable earth.

Police placed tarp around the site as three cranes worked for most of the afternoon to retrieve the man's body. The accident was reported at 10:30 a.m., and the worker's body was pulled from the trench at about 3:25 p.m., when he was pronounced dead.

Witnesses said about a half-dozen construction workers were at the site at the time of the accident. No other injuries were reported.

The project - an 8,289-square-foot parking garage and office complex - is situated in a largely residential area less than a mile from the beach near South Park. The three-level building will include two stories for offices and a garage below.

Workers from the city of Hermosa Beach maintenance yard, located a block away on Sixth Street, ran to the scene when they heard workers yell for help.

"They tried to dig around him, but it was very dangerous," said one worker, who didn't want to be identified. "The ground was still moving."

A cause of death has not been determined, but it is likely the man asphyxiated due to the amount of soil that fell on top of him, officials said. The Los Angeles County coroner is investigating.

The property is owned by David B. Shaw, a Palos Verdes Estates resident who runs a contracting company called David Shaw Concrete and Block. Shaw, also listed as the contractor, did not return a phone call seeking comment.

The project, approved by the Hermosa Beach Planning Commission in 2006, has been in the works for several years, city records show.

Shaw planned to occupy 1,825 feet of the building for storage, and lease the rest for artist or architectural studios, manufacturing and warehousing, according to his building permit application.

Cal/OSHA immediately issued a stop work order. Chasarik said work will not be allowed to resume until the problems with the site are fixed.

The state will likely issue a full report - and possibly citations - in a few months, she said.

Throughout the day Wednesday, dozens of nearby residents gathered near the site to watch the activity.

"The city workers were pretty shook up," said Derek Nalbandian, who lives a block away and said he heard commotion and went to the scene. "I can't imagine seeing something like that."