The blaze at 221 Nepperhan Ave. was reported at 3:15 a.m. Saturday.
The four people -- all civilians -- were taken to St Joes Hospital for smoke inhalation, said Thomas Fitzpatrick of the Yonkers Fire Department.
The Office of Emergency Management and Red Cross are on the scene for assistance.
The nine families needing relocation have gathered at the Nodine Hill Community Center, Fitzpatrick said.
This is a developing story. Check back to Daily Voice for updates.
Click here to follow Daily Voice New City and receive free news updates.