Six persons have been detained in connection with the gangrape of the girl, aged around 15. The offence took place on the ground floor of the housing society, they said.
"The alleged offence took place in the early hours today in Pestom Sagar area of Chembur," Tilak Nagar police station's senior inspector Bhagwat Sonavane said.
One of those detained is known to the girl.
The caretaker of the premises where the offence took place was untraceable and a search was on for him, police said.