The child was attacked by the group while waiting for a snake bite in a hospital near Lucknow in the northern province of Uttar Pradesh.
Police investigate the incident after she told her grandmother about the ordeal on Saturday night.
Local police officer Mahesh Srivastava confirmed that one man was in custody but the officers were still hunting for four more.
Investigators requested CCTV footage from the hospital to find out why she was left alone.
Mr. Srivastava said the girl had been 150 miles southwest of Lucknow for four days before the attack.
The incident is the latest in a series of high-profile sexual assaults that have shocked India in recent years and widespread protests against violence against women.
Earlier this year, the Indian government passed laws that imposed stricter penalties for those convicted of rape, including 20-year jail sentences and the death penalty for the rape of a child under the age of 12.
In 2012, the country was shaken by gang rape and the murder of a student on a bus in New Delhi, causing a backlash and causing women to speak out against sexual assault.
Despite increasing rallies and more serious laws, sexual assaults are still prevalent in a country where violence against women and children is being quietly accepted.
In August, a nine-year-old girl was raped at a Vashi private school, and in September, a 19-year-old student was kidnapped by three men and taken home by a school class in Haryana.
In one of the most shocking cases in India, 34 girls were raped in a children's home in the state of Bihar, the youngest victim being only seven years old.
The charity was supposed to be an animal shelter to protect vulnerable girls who had run away or been rescued from the streets, but the organization's head, Brajesh Thakur, was arrested along with nine other people.
He denies any wrongdoing and the police said one of the other defendants had fled.