"Shelter in place if on campus. All campus buildings on lockdown," the University of California Police Department at Berkeley (UCPD) tweeted, adding that the event with Milo Yiannopoulos had been cancelled.
Breitbart News is the online website where Steven Bannon, top advisor to US President Donald Trump, previously served as executive chairman. Bannon is said to be behind some of Trump's most controversial policies, including his restrictions on immigrants.
Campus police tweeted multiple requests for protesters to disperse. They also issued an alert to local residents, saying they "should stay away" from the area with a "major protest activity taking place."
Protesters threw fireworks at police officers, pulled down metal barricades, smashed windows and set fires outside the building where Yiannopoulos had been set to speak, the San Francisco Chronicle reported.
On his Facebook page, Yiannopoulos, who was banned last year from Twitter, said he was evacuated from the campus "after violent left-wing protestors tore down barricades, lit fires, threw rocks and Roman candles at the windows and breached the ground floor of the building."
Yiannopoulos had been expected to use the event to kick off a campaign against "sanctuary campuses" that have vowed to shelter undocumented students, the Chronicle reported.