Demonstrators are beaten up by police personnel in New Delhi. Reuters

The third day of what had been a peaceful demonstration against the law, passed by India's Parliament last week, descended into chaos Sunday afternoon. Three buses were set on fire, police officials said.

Chinmoy Biswal, a top police official, said that six police personnel were injured in the melee in an upscale enclave of south Delhi.

Student organizers blamed outsiders for the violence.

"We have time and again maintained that our protests are peaceful and non-violent,” they said in a statement. "We stand by this approach and condemn any party involved in the violence.”

The escalation came as authorities in India's northeastern state of Assam on the border with Bangladesh, where violence erupted after the law's passage. Demonstrators fear an influx of foreigners will dilute native Assamese people's political sway and culture. Five people have been killed in ongoing protests over the law that, for the first time in Indian history, grants citizenship on the basis of religion.

At Jamia Millia Islamia University in Delhi, where slogans such as "#SecularIndia” were graffitied on buildings, many students told reporters that the police fired tear gas inside the university’s library and beat up protesters before sealing all campus gates.

The massive gathering of student protesters at the Delhi Police headquarters is beginning to attract opposition politicians of various hues to raise their voice against the police crackdown on the Jamia Millia Islamia students on Sunday evening.

For some time, the sight of some protesters standing on barricades didn't actually looks like students as it was very to differentiate between the students and common people.

There was dismay writ large on the faces of many student protesters who were feeling that the politicians have hijacked their rightful place.

Meanwhile, political parties and politicians alike are losing no time tweeting their opinions on the student unrest.

Former union finance minister Yashwant Sinha tweeted, "This is the 1974 moment of Modi sarkar. The beginning of the end."

Sunday's protest at Delhi police headquarters after the students violence at Jamia Millia Islamia university and later the police crackdown, has gathered strength as more and more people from nearby places reached the spot.

Protest erupted on the campus of Moulana Azad National Urdu University (MANUU), here on Sunday night, against the police 'brutality' on students of the Jamia Millia Islamia University and the Aligarh Muslim University.

Dozens of students of the country's only Urdu university gathered on the campus around midnight and raised slogans against the police action on Jamia and AMU campuses. They expressed solidarity with the students of the two universities and demanded action against the policemen who entered the campuses and resorted to baton-charge on students.