The 34-year-old woman raped and brutalised inside a stationary tempo in suburban Mumbai's Sakinaka in the early hours of Friday has died while being treated at a local hospital.
A statement from Chief Minister Uddhav Thackeray's office decried the "shameful" and "highly condemnable" incident, and vowed to ensure the strictest punishment for the accused.
"This incident is highly condemnable... it shames humanity. The accused will be given the harshest possible punishment and a fast-track court will handle the trial," the statement said.
A Special Investigation Team (SIT) has been constituted to probe the case, said Mumbai Police Commissioner Hemant Nagrale, adding that prima facie evidence revealed only one accused was involved in the crime.
"An SIT has been formed to probe the case. Chief Minister has ordered fast track trial in the case. Unfortunately, the victim died during treatment this morning and we have converted section 307 (attempt to murder) of the Indian Penal Code (IPC) to section 302 (murder). The probe revealed there's only one person involved in the execution of the crime," said Mr Nagrale.
In a vile attack that bore a disturbing similarity to the assault on a young medical student in Delhi in 2012, the woman was sexually assaulted and tortured.
A team of police officers - alerted after the control room received an emergency call at 3.30 am on Friday - found her lying in a pool of blood on Khairani Road.
The caller said a woman was being beaten by a man, news agency PTI said.
She was rushed to the government-run Rajawadi Hospital for treatment.
Day time visuals from the area show a busy main road, with more than a moderate amount of traffic buzzing up and down. Disturbing CCTV footage has also been secured by the police; grainy visuals seem to show a man standing over what looks like body lying on the ground.
A PTI report said preliminary inquiries found bloodstains inside the tempo, which was parked by the roadside during the assault.
One accused - 45-year-old Mohan Chouhan - has been arrested, PTI said, adding he had been arrested under charges of rape and attempt to murder (which will now be revised to murder).
He was produced in court and sent to police custody till September 21.
The National Commission for Women has taken cognisance and expressed dismay at the "barbarity and atrocity" of the attack, directing the police "to immediately intervene.... an FIR must be filed".
The NCW urged charges of rape, murder and voluntarily causing grievous hurt, and asked police to complete inquiries in a fair and time-bound manner.
With input from PTI