The incident took place at Chandni Mahal area at around 8 pm and around 15 people still feared trapped under the debris, police said.
Eight persons were pulled out of the debris and taken to Lok Nayak Jaiprakash Narain Hospital where doctors declared three of them brought dead, hospital and police officials said.
Police said the building collapsed under the impact of an adjacent under-construction structure. Five injured are being treated at the hospital.
A seven-storeyed structure, built illegally, had collapsed in East Delhi last November, killing over 70 people and injuring many others.