Indian police have said a photo journalist in her early 20s was gang-raped in Mumbai yesterday.
The attack 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.
The woman has been admitted to hospital in south Mumbai, police said.
One man has been arrested and 20 police teams are pursuing four men who have been identified, said Mumbai Police Commissioner Satyapal Singh.
The attack took place in an abandoned textile mill in Lower Parel, a former industrial district that is now one of the city's fastest-growing neighbourhoods of luxury apartments, shops and bars.
The woman was out on assignment with a male colleague.
Women's safety in India has been in the spotlight this year following the 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 due to be passed on 31 August.
Closing arguments in the trial of the four adult suspects started yesterday.