Police in India are investigating allegations a four-year-old girl was gang-raped while being treated in an intensive care unit at a hospital in the country's north.

Key points: The child was being treated for a snake bite

The child was being treated for a snake bite One man is in custody but four others are allegedly involved

One man is in custody but four others are allegedly involved India recently approved the death penalty for child rapists

Local police official Mahesh Srivastava said that the girl told her grandmother she was raped by a hospital attendant and four others when she was alone on Saturday night.

He said one man was in custody and police were looking for others.

Police also have asked for CCTV footage and are trying to determine why the girl was left alone in the ICU.

Mr Srivastava said the girl had been in the hospital for four days and was being treated for a snake bite.

"Women have only one demand, the society should be violence free," read a placard held by protesters in New Delhi. ( AP: Altaf Qadri )

The hospital is located 250 kilometres south-west of Lucknow, the capital of Uttar Pradesh.

India has been shaken by a series of sexual assaults in recent years, including the gang-rape and murder of a student on a moving New Delhi bus in 2012.

That attack galvanised a country where widespread violence against women had long been quietly accepted.

Responding to widespread outrage over the recent rape and killings of young girls and other attacks on children, India's government earlier this year approved the death penalty for people convicted of raping children under age 12.

Sorry, this video has expired Protests and vigils have been held across the country following a string of violent assaults.

AP