The new-born was suspected to have been abandoned by her mother in the toilet at suburban Kanjurmarg, police said.
The baby was rushed to a hospital for medical aid, and later moved to a child care centre, they said.
On June 9, a woman spotted the crying baby with her face in the toilet hole, police said.
The woman pulled the baby out and alerted her own family and the police control room.
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The baby, who needed urgent medical treatment, was taken to a civic hospital.
"After her health improved, we took the baby to Vatsalya Trust where she could get proper care," Senior Police Inspector Ajinath Satpute told PTI.
Decisions about her welfare will be taken by the Child Welfare Committee, he said.
Police are yet to trace the newborn's mother.
However, a case has been registered against the unidentified mother under IPC section 315 (an act done with intent to prevent child being born alive or cause it to die after birth) and section 317 (exposure and abandonment of child under 12 years by parent or person having care of it), the official said.