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

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 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.

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

The hospital is located 250km southwest 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.

While the government has passed a series of laws increasing punishment for rape of an adult to 20 years in prison, it's rare for more than a few weeks to pass without another brutal sexual assault being reported.

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.