Indian police have arrested eight suspects over the gang-rape of four schoolgirls abducted from their convent boarding house in the country's east, officials say.

The suspects, armed with knives, were arrested on Tuesday.

They barged into the hostel on Sunday night and kidnapped the girls aged between 12 and 14, before assaulting them in a nearby forest in the tribal state of Jharkhand, a police officer said.

"We have made some arrests and we are interrogating eight persons accused in the case," Y S Ramesh, a police superintendent, told the AFP news agency.

"These girls are shocked and frightened after the incident," he said, adding that police would press for a speedy trial if the men were charged over the crime.

Teachers trapped

India faces intense scrutiny over its efforts to curb violence against women following the fatal gang-rape of a student on a bus in New Delhi last December which sparked major protests.

The school principal told police that the gang locked him and other teachers inside a room at the school run by a Christian missionary in the state's Pakur district.

The men then entered the dormitory and took away four girls, all belonging to a local tribal community, police said.

Ramesh said medical tests on the girls had confirmed that they were raped.

Mass protests erupted nationwide in December and January following the fatal gang-rape, which brought simmering anger about the treatment of women in India to the surface.

Parliament has passed laws aimed at better protecting women, including doubling the minimum prison sentence for gang-rape to 20 years.