Five people were injured when an unoccupied five-storey under-construction building tilted and rested precariously on another in Inderpuri on Saturday.
The building toppled on an adjacent four-storey house in JJ resettlement colony in Inderpuri, trapping five people, who were rescued by fire department personnel over an hour.
No one sustained any serious injury, said a fire department official.
A senior official of the North Delhi Municipal Corporation said the foundation of the building was very weak as it was built in just 25 square yards which is not sufficient space for a five-storey building.
It was constructed in just six months time and substandard material might have been used, he said.
The builder might have taken advantage of corporation officials as corporation staff are busy during these days and hurriedly erected the structure, he added.
He, however, said building plan is not needed for constructing houses in JJ colonies because the building plots are just 15-25 square yards.
The area has been cordoned-off. The debris from the collapsed structure was being removed and workers have been engaged to dismantle it.
Police said the owner of the building is being questioned.
A senior police officer said there are several other buildings in the area which are constructed in a similar fashion and have a very weak foundation.
The Inderpuri JJ Colony has around 3,000 houses and several of them been constructed on 25 to 30 square-yard plots. These plots were given to families in the 1960s by former prime minister Indira Gandhi.
The North Corporation is planning to launch a major crackdown on such buildings soon.
The incident has damaged five nearby buildings and cracks have developed in three of them.