A 40-year-old man died after inhaling toxic fumes while another person fell unconscious while they were repairing a sewer tank at the Delhi Jal Board (DJB) office in southeast Delhi's Okhla on Wednesday, police said.
The deceased has been identified as Suresh, they said.
Both the men were found lying inside the sewer, police said, adding they were not wearing any safety equipment.
"We were informed around 11:15 am from the Jal Board office about the incident. On reaching the spot, the police team found two men -- Suresh and Jagbir -- unconscious inside the sewer treatment plant," said Deputy Commissioner of Police (Southeast) RP Meena.
The Delhi Fire Services were informed and firemen pulled out the two men who were taken to a hospital, he said.
Suresh was declared dead by the doctors while Jagbir (43) is undergoing treatment, Meena added.
Suresh worked with SDV Engineering Associates Pvt Ltd and was called to the DJB office to repair a screw that had blocked the flow of water in the sewer. Jagbir, works at the office as a sweeper, according to police.
Police said that they found that another man named Murari (40) also tried to enter the sewer to rescue the men but could not help them, the DCP said.
Murari told the police that Suresh worked in the morning hours and was told to repair a screw inside the sewer, he said.
When the man went inside, he inhaled fumes and fell unconscious. After some time, Jagbir noticed that Suresh had not come out so he went inside the sewer to help him but also fell inside, he added.
Murari then tried to rescue both the men but came back and informed others, he said.
A case under sections of negligence resulting in death has been registered at Okhla police station against unknown persons, police said, adding that an investigation will done to identify the accused.