Three persons died after inhaling toxic gases while cleaning a sewer line here on Sunday afternoon, police said.
Deputy Commissioner of Police Romil Baaniya said the incident occurred in Lajpat Nagar area of south Delhi.
The Delhi government has ordered an inquiry into the incident.
Police identified the deceased as Joginder, 32 and Annu, 28, both residents of Khichdipur area, while the third who seemed to be in his mid-20s is yet to be identified.
Baaniya said that a police team reached the spot after being informed of the incident and took the three to All India Institute of Medical Sciences where they were declared dead.
Delhi Water Minister Rajendra Gautam tweeted: "I am very sad to know that 3 workers are expired during cleaning of sewer at Lajpat Nagar I have set up an inquiry."
He also said that the workers were neither Delhi Jal Board employees nor authorised by it.