The attack on Thursday night triggered protests and an outcry on social media, with many users shocked that it took place in Mumbai, widely considered to be India's safest city for women.
One man was arrested on Friday and 20 police teams were pursuing four men who had been identified, said Mumbai Police Commissioner Satyapal Singh.
"Mumbai police will do its best to collect all the evidence — clinching evidence, scientific evidence — so that a fool-proof case is made out in the court, and they get maximum punishment," Singh said. "We will also request the government that this case be conducted in a fast-track court."
In rowdy scenes in the upper house of parliament, opposition lawmakers accused the government of not doing enough to protect women, despite tougher sex crime laws brought in this year.
The victim, who is in her early 20s, was admitted to hospital in south Mumbai, where she was in stable condition, a hospital official told Reuters by e-mail.
The attack took place shortly before sunset in an abandoned textile mill in Lower Parel, a gritty former industrial district that is now one of the city's fastest-growing neighbourhoods of luxury apartments, malls and bars.
The woman was at the mill on an assignment with a male colleague. The pair were separated by the attackers and her colleague was tied up with a belt while she was assaulted, Singh said.
Several dozen mainly male supporters of the right-wing Shiv Sena political party gathered with flags and banners outside the police station where the case was filed. A further protest was called for later in the afternoon.

Verdict awaited in New Delhi bus gang rape

Women's safety in India has been in the spotlight this year following the brutal gang-rape of a 23-year-old student on a moving bus in New Delhi in December, which led thousands of Indians to take to the streets in protest. The woman died of her injuries two weeks later in a Singapore hospital.
The trials of the four men and one juvenile accused of the December attack are expected to conclude within the next three weeks. The verdict on the juvenile suspect is set for Aug 31.
Closing arguments in the trial of the four adult suspects started on Thursday.
Following public outcry over the Delhi attack, India introduced tougher rape laws in March, which include the death penalty for repeat offenders and for those whose victims were left in a "vegetative state".
In contrast to Delhi, Mumbai has long been considered a safer place for women to travel alone, even at night."(Mumbai) has this sense of security ... but these things make us feel that maybe we are not really that safe," said A. L. Sharada, director of Population First, a Mumbai-based NGO that works on women's rights issues.
"Women should be able to move freely and take up work. Why should we be worrying about something bad happening to us all the time?"

Indian journalist, 22, gang raped in Mumbai in case that has echoes of December New Delhi rape

(Rafiq Maqbool/ Associated Press ) - Indian policemen inspect the site where a 22-year-old woman was gang raped in Mahalaxmi area in Mumbai India, Friday, Aug. 23, 2013. The young woman photojournalist was gang raped while her male colleague was tied up and beaten in India’s business hub of Mumbai, police said Friday. The case was reminiscent of the December gang rape and death of a young university student in the Indian capital that shocked the country.
NEW DELHI — A 22-year-old photojournalist was gang raped while her male colleague was tied up and beaten in an isolated, overgrown corner of India’s business hub of Mumbai, police said Friday. The case was reminiscent of the December gang rape and death of a young university student in the Indian capital that shocked the country.
The latest attack took place Thursday evening in Lower Parel, a onetime textile-manufacturing neighborhood of south Mumbai that over the past decade has changed dramatically. Today, upscale malls, trendy restaurants and super-luxury condominiums sit side-by-side with abandoned textile mills and sprawling slums.

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Police said the Indian woman was on assignment for a magazine to take pictures of the neighborhood when five men confronted her and her colleague at about 7 p.m. After initially offering to help her get permission to shoot inside a crumbling, isolated building, the men became aggressive and accused the male colleague of being involved in a local crime.
When he denied involvement in the crime, they tied his hands with a belt and took the woman to another part of the compound and took turns raping her, Mumbai’s police commissioner, Satyapal Singh, told reporters.
Police on Friday arrested a suspect in the attack who named and identified the other four men, Singh said. While police have released sketches of the four men, Singh would not give their names or other details, saying authorities did not want to give them any warning that they were being sought. Singh said the men may have been local drug dealers.
The woman was in stable condition in a hospital. Police declined to say who she was working for at the time of the attack.
The assault comes amid heightened concerns about sexual violence in India. The gang rape and death of the student on a bus in New Delhi in December had shaken a country long inured to violence against women and sparked protests demanding better protection for women.
In response, the government passed a stringent law increasing prison terms for rape and making voyeurism, stalking, acid attacks and the trafficking of women punishable under criminal law.
About 1,000 people, including members of several local journalists’ associations, gathered Friday evening in south Mumbai to stage a silent protest. Some wore black armbands, while others carried placards reading “Stop rape” and “City of shame.”
The attack was also discussed in India’s Parliament, where junior Home Minister R.P.N. Singh told lawmakers that the government had asked the state of Maharashtra, of which Mumbai is the capital, for a detailed report on the attack.
He said the federal government had recommended that the “harshest” punishment be handed down to anyone found guilty in the case.
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