The latest building to collapse in Huruma, Nairobi killing three people had been marked for demolition by the National Construction Authority.
Mathare sub-County Deputy Commissioner Patrick Mwangi said some of the tenants had sneaked back into the condemned building and had been staying there for months.
Authorities said that rescue operations were delayed because of congestion in the densely populated estate.
Rescue teams had to demolish nearby structures to access site of the collapsed building.
The National Disaster Management Unit Deputy Director Pius Masai said rescue efforts had also been hampered by Kenya Power’s slow response to cut off “illegal” electricity connection to the building.
Eleven of the 12 families that had been staying in the building have not yet been accounted for.