An Indian court convicted six men Thursday of gang-raping and murdering a student as she walked home after an exam in 2013, in a case that sparked outrage over women's safety.

Security was tight outside the court in the eastern city of Kolkata for the verdict, with chanting protesters demanding justice and scuffling with police.

Senior public prosecutor Dipak Ghosh told AFP that six accused were convicted of gang-raping the 21-year-old woman, as well as murder, interfering with evidence and other charges.

Judge Sanchita Sarkar told the packed court that two others "are acquitted due to lack of evidence".

"The... punishment will be announced after hearing the convicts on Friday," she said.

The six face punishments ranging from 20 years in jail to the death penalty.

The gang attacked the university student as she returned home to her village, 50 kilometres (30 miles) northeast of Kolkata, in June 2013.

The victim, who cannot be named for legal reasons, was grabbed after getting off the bus before being dragged to a nearby abandoned farm.

She was found gagged and laying in a pool of blood in a field the next morning. Evidence showed she had been repeatedly raped.

The attack triggered anger in West Bengal state and came just months after the fatal gang rape of a student in Delhi in December 2012 that shone a global spotlight on violence against women in India.

The 2012 incident led to an overhaul of India's rape laws including speeding up of trials and tougher penalties for offenders, but high numbers of assaults persist.

About 200 protesters gathered outside the court for Thursday's verdict demanding justice, an AFP reporter said.

One policeman was injured in scuffles as protesters tried to enter the court complex, police said.