Police in India have entered the campus of one of the country's most prestigious universities after reports of masked men attacking students.
About 20 students are said to have been injured at the Jawaharlal Nehru University (JNU) in the capital Delhi.
Images on Indian TV show masked people wielding sticks and the student union president bleeding from a head wound.
The cause of the trouble is unclear. The university recently saw protests over a controversial citizenship law.
There were also violent clashes at JNU last year over a rise in hostel fees.
The student union blamed the latest violence on the Akhil Bharatiya Vidyarthi Parishad (ABVP), a right-wing student body linked to India's governing BJP political party. However, the ABVP said that its members had been attacked by left-wing groups, and some had been injured.
One member of staff said masked men armed with stones and sticks had attacked students and teachers on Sunday evening.
"These were not small stones, these were big stones that could have broken our skulls," Professor Atul Sood told NDTV.
"I fell on the side and when I came out, I saw cars completely vandalised, including my car."
Professor Sood said about 50 teachers and 200 students had been holding a meeting on the campus when the masked attackers walked in.
He said the violence was unlike anything the campus had witnessed before.
Education Minister Ramesh Pokhriyal Nishank condemned the violence calling it "extremely worrying and unfortunate".
"I appeal to all students to maintain the dignity of the university and peace on campus," he added.
Government Finance Minister Nirmala Sitharaman said the scenes of violence were "horrifying".
Horrifying images from JNU — the place I know & remember was one for fierce debates & opinions but never violence. I unequivocally condemn the events of today. This govt, regardless of what has been said the past few weeks, wants universities to be safe spaces for all students.— Nirmala Sitharaman (@nsitharaman) January 5, 2020
West Bengal Chief Minister Mamata Banerjee called the attack a "heinous act" and a shame on democracy.
The Students Federation of India said it would stage rallies in Delhi on Monday in protest at the "barbaric attack" at the JNU.
A police spokesman said university authorities had asked for their assistance.
"We were informed that there was a clash between two groups of students," a statement said.
"After we received written request from the JNU administration, we entered the campus and restored peace."