Three persons were extricated from under the debris and taken to hospital, where two of them, including the building's owner, were declared dead and the third admitted for treatment, police said.
The incident occurred in south Delhi's Taimoor Nagar around 9.45 am.
"The building is 50-60 years old. During the rescue operation, it was found that the building belonged to Dhruv Kumar, a retired government servant," Deputy Commissioner of Police Romil Baniya said.
"They were rushed to AIIMS where Montu Mandal was admitted with external injuries, while Dhruv Kumar and Krishan Mandal were declared brought dead," Mr Baniya said.
The building collapsed when they were surveying it from the inside. Mr Kumar had hired the two for demolition work, he said.
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