Police in Portland, in the northwestern U.S. state of Oregon, declared a riot Saturday night after demonstrators threw several Molotov cocktails into the street.

The police told the crowd of hundreds their demonstration was considered a riot and ordered the people to disperse immediately. In Oregon, a riot is defined as six or more people engaging in “tumultuous and violent conduct” that creates “a grave risk of causing public alarm.” It’s illegal for police in Oregon to use tear gas unless a gathering has been declared a riot.

Police said protesters threw multiple “fire bombs” and that at least one person was injured. Twitter footage from protesters and members of the media showed a man who appeared to be a protester with his feet and lower legs ablaze.

Other video clips showed clouds of what observers said was tear gas floating through a residential neighborhood.

Activists in Portland have taken to the streets for 100 consecutive days to show support for the Black Lives Matter movement and to protest what they see as social injustices that have afflicted the United States for decades. Some of the protests have drawn thousands.

The U.S. has been roiled by protests since the death earlier this year of George Floyd, a Black man who died while in police custody in Minneapolis, in the Midwestern state of Minnesota.

Floyd had been stopped on suspicion of passing a counterfeit $20 bill.  His death has come to symbolize what many see as the “systemic racism” that they see as permeating American society.