A two-week-old baby was killed when his mother was attacked and gang raped on a bus in India, local police have said.

The 28-year-old woman said she had been travelling through the country's northern Uttar Pradesh state, returning home to Rampur after visiting her sister in Shishgarh.

She was assaulted on the bus after all other passengers got off.

"I was returning after visiting my sister, they assaulted me and during the scuffle my child died," she told the media.

Bareilly senior Superintendent of Police, RK Bhardwaj, said the body of the 14-day-old baby boy had now been sent for post mortem.

Reports suggest the woman's elder child, a three-year-old girl, had hidden on the bus while the attack took place and was not harmed.

A manhunt was launched to find the men responsible, and local media today reported two men had been arrested and charged with gang rape and culpable homicide.

The incident has been widely condemned by politicians and women's rights activists, who argued the men should be charged with murder.

India has struggled in recent years to address criticism of its handling of sex attacks against women, with rapes and assaults regularly making the headlines.

Earlier this week, a 15-year-old girl died after being raped and set on fire in New Delhi, suffering 95 per cent burns to her body.

And in 2012, 23-year-old Jyoti Singh was gang raped and tortured by six men on bus in Delhi before being left to die at the roadside, sparking major protests across the country.

According to an annual report by the National Crime Records Bureau, there were 337,922 reports of rape, molestation, abduction and cruelty by husbands against their wives in 2014.

Meanwhile, 86 per cent of rapes in India were carried out by close family members such as fathers, brothers and uncles, as well as neighbours, employers, co-workers and friends.