A 17-year-old girl was allegedly gang-raped on a moving bus in Bihar, police said on Wednesday.

Four people were arrested in connection with the incident that happened on Tuesday, they said.

"The girl was waiting at the Motihari bus stand in East Champaran district for a bus to Bettiah in West Champaran. The bus driver told her that it was going to Bettiah and she hopped on it," sub-divisional police officer (Bettiah-Sadar) Mukul Pandey said.

"She was given a spiked drink on the bus, following which she fell unconscious. She told police that she was gang-raped after that," he said.

The girl told the police that when she regained consciousness she found herself on the bus with its doors locked.

"The accused had locked her inside the bus and fled. People who were passing by opened the door and informed the police," another police officer said.

Four people, including the driver, conductor and helper of the bus, were arrested in connection with the incident, police said.

The medical examination of the girl was conducted at the government hospital in Bettiah, they said.

"Now, forensic experts have been called for the analysis of the evidence gathered. The bus has already been seized," Pandey said.

A case was registered under relevant sections of the IPC, besides the Protection of Children from Sexual Offences (POCSO) Act, he said.