The 9 were evacuated to Neema Hospital off Thika Road after the incident which occurred at about 11am.
Kasarani OCPD Francis Sang' said at least s 6 workers were still trapped under the rubble.
Speaking at the scene, Sang said the collapse may have been due to faults related to a hurried construction.
A vehicle was also damaged when the six-storey residential building collapsed. Kasarani AP and General Service Unit officers and the National Youth Service are part of the rescue team.
In January, Nairobi Governor Evans Kidero issued a warning to contractors who did not meet the approved construction standards.
Kidero made the remarks following the collapse of a building in Huruma in which five died, and another in Makongeni in which four were killed last December.
