A man in his 50s who went missing on Sunday while inspecting a wastewater pipeline inside a manhole in Incheon was found dead.

According to Incheon fire authorities, the 52-year-old employee of a pipeline inspection and management company was found dead Monday morning at a sewage treatment plant connected to the pipeline.

After receiving a call Sunday morning that two people had fallen unconscious inside a manhole, authorities rescued the head of the inspection company, who was in his 40s and found without vital signs, but could not locate the missing worker.

The police and fire authorities suspect the two people had suffered toxic gas poisoning after confirming hydrogen sulfide and carbon monoxide from the pipeline.

The police intend to request an autopsy by the National Forensic Service to determine the exact cause of the worker's death.