A planned talk at the University of California-Berkeley by polarizing Breitbart News editor Milo Yiannopoulos was canceled Wednesday evening after protesters threw smoke bombs and flares at the student union building where he was scheduled to speak.
Mr Yiannopoulos is an outspoken supporter of President Donald Trump.
Hundreds of students rallied and were faced by riot police. At least one fire was started and police fired tear gas. The campus is now on lockdown.
Criticised as racist and misogynist, Mr Yiannopoulos was banned from Twitter.
He had led a campaign against Ghostbusters actress Leslie Jones.
Berkeley College Republicans sponsored Mr Yiannopoulos’ visit.
Their spokesman Pieter Sittler said they didn’t agree with everything he said, but “he gives a voice to repressed conservative thought on American college campuses”.
UC Berkeley stressed that it had not invited Mr Yiannopoulos, but had rejected earlier calls to cancel the event.
Students protested peacefully earlier in the day, but later some broke windows at the hall where the talk was due to be held, threw smoke bombs and started a fire on Sproul Plaza.