Police have declared a riot outside a just center, next to a federal courthouse.
Police said Wednesday night that some in the crowd were engaging in criminal activity, setting fires and exploding fireworks outside the federal building.
They told people to leave and used tear gas in an attempt to push people out of the area.
Protests have assembled nightly in Portland since the killing of George Floyd in late May.
Floyd, a Black man, died after a white officer pressed a knee to his neck. Protests had dwindled but grew again after President Trump sent federal agents in early July. They have since withdrawn.
Some recent gatherings have been smaller and targeted local police facilities.
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