Indian police were searching New Delhi Monday for the men who gang-raped a 23-year-old-student and threw her off a bus in an attack that has sparked fresh concern for the safety of women in the city.
The woman accompanied by a male friend boarded a bus on Sunday night and was attacked by at least four men and gang-raped, police said.
Some media reports said the attackers also included staff of the bus.
The victim's companion was battered with iron rods before the men took turns and raped her, police officials said.
The couple were then thrown off the moving bus, seriously injuring the woman, they said.
"When they boarded the bus, there were a few other men as well in the vehicle," area police chief Chhaya Sharma told reporters.
"As of now, we can confirm the involvement of four men," she said, adding police artists have drawn sketches of the attackers from descriptions given by the victims.
Chief Sharma said the female victim was in intensive care in a city hospital where her companion is also being treated.
The attack sparked new calls for greater security for women in New Delhi, which registered 568 rapes in 2011 compared to 218 in India's financial capital Mumbai the same year.
"This is a shocking incident. I hope that the guilty are punished for the heinous crime," said Kiran Walia, women and child development minister in the Delhi state government.
Delhi Chief Minister Sheila Dikshit promised "precautions" to prevent such attacks in the future but did not elaborate.
New Delhi's shiny new metro has reserved a carriage in every train for woman while several police stations in university and other areas have all-female staff to try and stem rising crime against women.
Rape cases in India more than doubled between 1990 and 2008, according to official data.