The University of California at Berkeley has cancelled a talk by the editor of the right-wing Breitbart News website, Milo Yiannopoulos, after student protests against his visit.
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, as the campus was put on lockdown.
There are no reports of arrests or serious injuries.
Mr Yiannopoulos’s comments have been criticised as racist and misogynist.
Last year he was banned from Twitter after leading a campaign against Ghostbusters actress Leslie Jones.
Berkeley College Republicans sponsored Mr Yiannopoulos’s 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.
Last November, Mr Yiannopoulos’s old school cancelled a talk he had been due to give.
The Simon Langton Grammar School for Boys in Canterbury, England, said they took the decision partly because of the threat of demonstrations.