The two accused have been arrested.
The incident came to light in the wee hours today when the woman, a native of Uttar Pradesh, was spotted lying in a duct of the building in the Pydhonie area here.
After getting information about the incident, the Pydhonie police rushed to the spot and admitted the woman in a state-run hospital.
"The Pydhonie police has registered an offence of gangrape and arrested the two accused. Further investigation is on," Deputy Commissioner of Police, Zone-II, Dnyaneshwar Chavan said.
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The accused had brought her to Mumbai 10 days back on the pretext of getting her employment, he said.
Both of them stayed in Bhiwandi township of the neighbouring Thane district for eight days where also she was allegedly raped by him, he said.
They came to the building in Pydhonie yesterday at the godown cum residence of the other accused, he said.
At around 4 AM , she was spotted in the duct of the building by some residents.
Police said the woman fell in the duct while trying to run away from the house while the two accused were asleep.
She suffered serious injuries and has been admitted in a hospital, the official said.