Two minor girls, both sisters, were allegedly raped by four men at Kenduadih, about 15 km from Jharkhand's Dhanbad, police said on Wednesday.
The main accused, a friend of the elder sister, had called her to meet him on Tuesday evening, the Superintendent of Police of Dhanbad (Rural) district Aman Kumar, said.
The 15-year-old girl took her 12-year-old sibling to a place where her friend had called her, the official said.
After reaching the designated spot, the elder sister's friend took both the girls to a school, where three other men joined him and all of them allegedly raped the sisters, the police officer said.
The girls were sent to Patliputra Medical College Hospital (PMCH) for medical examination, he said.
Since both of them were seriously injured, the doctors there admitted them.
The family of the girls came to know about the incident after they reached home around 9 pm on Tuesday, the Officer-in-Charge of Kenduadih Police Station, Veer Kumar, said.
The family immediately reported the matter to the police station, he said.
A First Information Report or FIR was lodged against four men on Wednesday, Mr Kumar said.
The police has launched a search operation to arrest the four accused, whom the girl named in her complaint to the police.
The accused are in their early twenties, Mr Kumar said, adding, the mother of the survivors works as a domestic help at some houses in Nayadih area under the jurisdiction Kenduadih police station.
He also said that the doctors at the PMCH, after medical examination, confirmed that both the girls were gang-raped.