Violent protests have broken out at the University of California at Berkeley over a scheduled speech by the editor of far right organisation Breitbart News.
The campus has been put on lockdown after protesters threw smoke bombs, broke windows and lit a bonfire in the university square.
Riot police have been called in and there have been reports of clashes.
They are angry over a visit to the university by Milo Yiannopoulos, who is linked to the so-called "alt-right" movement.
Mr Yiannopoulous' speech was cancelled.
It is the second time in two weeks rowdy protests forced the cancellation of one of his planned addresses.
