At least three people were trapped on Monday, after a building under construction collapsed in Gachie, Kiambu county.
Witnesses and police said the structure had been built up to the fifth floor, and labourers were working on the sixth one when it collapsed on Monday afternoon along Muuru Road.
Several workers managed to escape the rubble soon after the 3pm incident.
Those who escaped said they had sustained injuries.
It is not clear the exact number of people trapped in the debris.
The building was meant to be a residence.
Kiambu police boss Ali Nuno said a rescue mission is ongoing and no death has been reported.
Nairobi and Kiambu are among areas experiencing a construction boom with many buildings having more than 10 floors.
There have been concerns of structures being constructed without proper supervision.
Last week, nine people died after a crane accident in Nairobi’s Hurlingham area.