KOLKATA (AFP) - A court in eastern India sentenced five men to 20 years imprisonment on Friday for raping and setting ablaze a schoolgirl who later died, a senior official said.

The 16-year-old was sexually assaulted twice in October by half a dozen men near her family's home in the town of Madhyamgram, 25km north of Kolkata, the capital of West Bengal state.

"A fast-track court on Friday sentenced five people in Madhyamgram gang-rape case to 20 years in jail," Manjit Singh, the state's chief public prosecutor told AFP.

Six men were arrested and charged over the attacks after the girl's death in a hospital on New Year's Eve last year. One of them was freed after he agreed to testify against his co-accused.

The girl's father, a taxi driver from Bihar, one of India's most impoverished states, had brought his family to West Bengal a few months before his daughter's death in the hope of better prospects.

The second rape of the teenager by the same gang of men occurred as she was returning home with her family after reporting the first attack at a police station.

Senior police officer from West Bengal, Anant, who uses only one name, told AFP the teenager, who cannot be named for legal reasons, was pregnant at the time of her death.

The victim's family had alleged that a member of the gang who attacked the girl had threatened dire consequences if the police complaint was not withdrawn.

The same day the threat was made in December, the victim was set ablaze in her own home, police said.

The men were convicted on the basis of the girl's dying declaration in hospital.

Her death sparked street protests in Kolkata as well as in New Delhi.

India has become more sensitised to the issue of violence against women since the brutal gang-rape and murder of a 23-year-old woman on a bus in Delhi in 2012.

Parliament has since passed tougher laws to punish rapists.

Activists say rape victims often face severe threats and intimidation from their attackers while police frequently discourage them from lodging complaints.