A subcontractor engaged in cleanup work at the meltdown-hit Fukushima No. 1 power plant died Friday after a hole he was digging collapsed, burying him alive.

“We are truly sorry for his loss and would like to offer our deepest sympathy,” Tokyo Electric Power Co. spokesman Masayuki Ono said at an evening news conference held at the beleaguered utility’s headquarters.

The man, who was in his 50s, is the first casualty of the plant’s decommissioning process. According to Tepco, as the utility is known, the man was in a 2-meter deep hole checking the foundation of a building where solid waste was being stored when he was enveloped by earth and sand at around 2:20 p.m.

More than a dozen other co-workers dug him out. But after being taken unconscious to the plant’s emergency medical center, his heart showed no electrical activity and he was declared dead at a hospital at 5:22 p.m., Tepco said.

Tepco said the police are investigating the accident and that the utility is unclear on the details of what happened.

Once the police investigation is finished, Ono said Tepco will review the findings in order to prevent another one in the future.

He said the workers were checking the building’s foundation to see how badly it was damaged by the 9.1-magnitude offshore mega-quake of March 2011. It wants to use the building to also store waste generated by the decommissioning process.